Official Addressing issues with missing references

volblob73 · May 15, 2020

We finally have a fix to an elusive issue that we know has caused frustration for many of you for a while. MonoBehaviour-based components as well as ScriptableObjects would lose references to other objects under certain conditions when the scripts they were based on temporarily didn't compile.

This could for example happen under the following conditions:

A team member fetches updates from version control where a script component has a new field and a Prefab that uses the script has a reference to another object assigned in that field.

However, due to local changes, the updated script doesn’t compile. This means the Prefab cannot import and so the added field is not present on the Prefab.

Once the compile error is fixed, a reimport of the Prefab can make the reference appear again. Unity keeps track of missing imports of Prefabs so it can automatically reimport them once the compile errors have been fixed. However, this information about missing imports is lost if the editor is restarted. In this case, the reimport does not happen automatically after all, and the reference remains missing even though there are no longer any compile errors.

Usually, the issue could be worked around by reimporting the affected Prefabs or other objects manually. However, tracking down the issue is not always trivial, and is made worse by the fact that it can manifest differently for different people working on the same project. Some of you have resorted to simply reimporting all Prefabs to be safe, which can take a while, especially for large projects.

A robust Asset dependency-based fix
The fix required introducing a new form of dependency in the Asset Database. Prefabs and other Assets now have a script type dependency on the MonoBehaviors and ScriptableObjects they contain instances of. Like with other Asset dependencies, this means that if a script type is changed, the Assets that depend on that script are reimported.

Luckily, it's not simply any edit of a script that causes dependent Assets to be reimported. It only happens if the fields of the script change, meaning fields are added or removed, or existing fields change name, type, or order. Changes to methods or properties won't cause any imports of dependent Assets to happen.

This change is needed because the imported result of Prefabs and other types that contain MonoBehaviors or ScriptableObjects depend on the fields of those scripts. So when the fields on those scripts change, a reimport must happen for the imported result to reflect those changes to the scripts.

It’s worth being aware that the new dependency will cause Prefabs to get re-imported upon script changes in cases where it didn’t happen before. This is a necessity of the more robust way of ensuring Prefabs get imported when they need to, in order to avoid missing references.

Versions of Unity with the fix
The fix will be coming to Unity 2020.1.0b10. Additionally, we are backporting it to Unity 2019.3, where it should become available in a couple of weeks. Since the fix depends on infrastructure that’s part of AssetDatabase v2 which was introduced in 2019.3, it’s not possible to backport the fix further back than 2019.3.

rskorski-wizards · May 15, 2020

We are very much looking forward to this fix in 2019.3! You mentioned that it depends on in AssetDatabase v2 infrastructure, does that mean our project will have to upgrade to v2 in order to benefit from the fix?

volblob73 · May 16, 2020

Yes, you need to use Asset Database v2 for this fix. Any specific reason why you are using v1?

volblob73 · May 20, 2020

Fix will be available in 2019.3.15f1.

Xarbrough · Jun 12, 2020

This is great news! Is the fix also on 2019.4 LTS?

Edit: Yes it is!

SteenLund · Jun 12, 2020

@Xarbrough Yes it is

KAJed · Jun 29, 2020

volblob73 said: ↑

Yes, you need to use Asset Database v2 for this fix. Any specific reason why you are using v1?
Click to expand...

I have found v2 to still be incredibly unstable and makes my projects unable to import even in some of the most basic circumstances (ie: small project, small number of packages).

As such I have not been able to recommend moving to v2 for my team.

OAT_PICKER · Jun 30, 2020

My team have also found v2 to be unstable, regularly hanging on launching the editor.

We really need this missing references bug fix, but cannot update to v2 in its current state.

volblob73 · Jul 24, 2020

@KAJed @OAT_PICKER
Have you reported the issues you have had? I can then have a look at them. We do have bugs in v2, but generally we are getting good feedback on v2.

KAJed · Jul 24, 2020

volblob73 said: ↑

@KAJed @OAT_PICKER
Have you reported the issues you have had? I can then have a look at them. We do have bugs in v2, but generally we are getting good feedback on v2.
Click to expand...

Yes. However, the core issue for me appears to be that triggering another load of any kind from inside an assembly load causes it to hang indefinitely on a mutex lock. I have pretty detailed information that I went over with the bug rep but felt like they misunderstood the problem. I diagnosed the problem with the lead on Odin Inspector since that particular asset was exhibiting the behaviour. The "fix" for it seems rather messy and we both felt like it shouldn't be needed.

volblob73 · Jul 30, 2020

@KAJed do you have a case number for that issue?

KAJed · Jul 30, 2020

volblob73 said: ↑

@KAJed do you have a case number for that issue?
Click to expand...

My case number for the issue is 1263658. There were unable to reproduce the issue in house but for me it was 100% repro.

volblob73 · Aug 4, 2020

@KAJed your case got marked as a duplicate other another case (1260657). This other case has just been fixed. Fix is available 2020.2 and should be available for 2020.1 and 2019.4 very soon.

waldgeist · Dec 9, 2020

We're on 2019.4.15f1 and experiencing broken prefab references quite often:
https://forum.unity.com/threads/broken-references-in-nested-prefabs.1019233

Only forcing Unity to rebuild its Library fixes those references. It seems as if there's still a pretty annoying bug in the asset referencing system somewhere.

rt_jscott · Dec 23, 2020

What date and version was the proposed fix for this?
I am having this problem often as well.
I am on 2019.4.9f1 but the release notes don't include date and the posts here only include dates.

Rodolfo-Rubens · Jan 21, 2021

I'm having this same problem on 2019.4.17f1... The prefab itself is okay on prefab mode, no missing child-prefabs, but when dropped in the scene they are 'missing prefabs'...

deLord · Jan 30, 2021

Not sure if this is the exact problem mentioned in the OP but I get a NPE in my script

Code (CSharp):

Destroyer dstr = Instantiate(Resources.Load("Prefabs/Destroyers/myprefab"), sometransform) as Destroyer;

if (dstr.someBool) ... // dstr null

but then the object is instantiated correctly in the scene. Using 2019.4.18f1 LTS

KAJed · Jan 30, 2021

deLord said: ↑

Not sure if this is the exact problem mentioned in the OP but I get a NPE in my script

Code (CSharp):

Destroyer dstr = Instantiate(Resources.Load("Prefabs/Destroyers/myprefab"), sometransform) as Destroyer;

if (dstr.someBool) ... // dstr null

but then the object is instantiated correctly in the scene. Using 2019.4.18f1 LTS
Click to expand...

In this case you're getting an error because you're casting directly to a component type. If that is a prefab then you need to GetComponent on it instead.

Carpet_Head · Feb 23, 2021

Looks like 2020.2.4 has caused a regression in this issue and it is happening again

TextusGames · Feb 27, 2021

@volblob73

The issue with missing nested prefabs in scene is still here in 2019.4.18 LTS
(It is possibly happens if not exit from unity before git check out / pull).

mahdi_jeddi · Jun 25, 2021

Just upgraded the project from 2020.3.12 to 2021.2.b1 and got missing references in the nested prefab in an object in the scene.

waldgeist · Jul 21, 2021

It's getting even worse. Now also localization string references are affected. This is really, really annoying. My work-around so far is to purge Unity's cache folders (like `Library`) before doing a production build. This typically restores all broken links. But dare you if you forget to do it. It might render your complete app unusable.

TextusGames · Jul 23, 2021

We managed to overcome this issue in builds.

In our build pipeline we call method to reimport all prefabs (at earliest stage).

Code (CSharp):

public static void ReimportAssets(string searchFilter)

{

var timeBeforeSearching = DateTime.Now;

// Finding assets

var objectGuids = AssetDatabase.FindAssets(searchFilter);

var objects = new Object[objectGuids.Length];

for (var i = 0; i < objectGuids.Length; i++)

{

var objectGuid = objectGuids[i];

var objectPath = AssetDatabase.GUIDToAssetPath(objectGuid);

var loadedObject = AssetDatabase.LoadAssetAtPath<Object>(objectPath);

objects[i] = loadedObject;

}

// Selecting assets and executing Reimport

Selection.objects = objects;

EditorApplication.ExecuteMenuItem("Assets/Reimport");

Debug.Log($"[{searchFilter}] Assets were imported. [{(DateTime.Now - timeBeforeSearching).Duration()}]");

}

Code (CSharp):

ReimportAssets("t:Prefab");

And this code (if you call it before build, (in our case it is called automatically)) solves missing reference problem in builds.

Clearing Library folder is also valid solution (but it takes much longer time).

D12294 · Jan 23, 2022

Hello everyone,

I have the same Issue on a cloned project with unity 2021.2.7f1 with following setup: I developed on PC, got a error free compile state, uploaded the project to Azure DevOps, then cloned the project on a Mac in terminal via git clone <clonepath> and after opening the project in unity all sprite references are missing. I really have no idea whats going on. I use the following git ignore file

Code (CSharp):

# This .gitignore file should be placed at the root of your Unity project directory

#

# Get latest from https://github.com/github/gitignore/blob/master/Unity.gitignore

#

/[Ll]ibrary/

/[Tt]emp/

/[Oo]bj/

/[Bb]uild/

/[Bb]uilds/

/[Ll]ogs/

/[Uu]ser[Ss]ettings/

# MemoryCaptures can get excessive in size.

# They also could contain extremely sensitive data

/[Mm]emoryCaptures/

# Asset meta data should only be ignored when the corresponding asset is also ignored

!/[Aa]ssets/**/*.meta

# Uncomment this line if you wish to ignore the asset store tools plugin

# /[Aa]ssets/AssetStoreTools*

# Autogenerated Jetbrains Rider plugin

/[Aa]ssets/Plugins/Editor/JetBrains*

# Visual Studio cache directory

.vs/

.vsconfig

# Gradle cache directory

.gradle/

# Autogenerated VS/MD/Consulo solution and project files

ExportedObj/

.consulo/

*.csproj

*.unityproj

*.sln

*.suo

*.tmp

*.user

*.userprefs

*.pidb

*.booproj

*.svd

*.pdb

*.mdb

*.opendb

*.VC.db

# Unity3D generated meta files

*.pidb.meta

*.pdb.meta

*.mdb.meta

# Unity3D generated file on crash reports

sysinfo.txt

# Builds

*.apk

*.aab

*.unitypackage

# Crashlytics generated file

crashlytics-build.properties

# Packed Addressables

/[Aa]ssets/[Aa]ddressable[Aa]ssets[Dd]ata/*/*.bin*

# Temporary auto-generated Android Assets

/[Aa]ssets/[Ss]treamingAssets/aa.meta

/[Aa]ssets/[Ss]treamingAssets/aa/*

######################################################

# macOS specific ignores

######################################################

# General

.DS_Store

.AppleDouble

.LSOverride

# Icon must end with two \r

Icon

# Thumbnails

._*

# Files that might appear in the root of a volume

.DocumentRevisions-V100

.fseventsd

.Spotlight-V100

.TemporaryItems

.Trashes

.VolumeIcon.icns

.com.apple.timemachine.donotpresent

# Directories potentially created on remote AFP share

.AppleDB

.AppleDesktop

Network Trash Folder

Temporary Items

.apdisk

######################################################

# Windows specific ignores

######################################################

# Windows thumbnail cache files

Thumbs.db

Thumbs.db:encryptable

ehthumbs.db

ehthumbs_vista.db

# Dump file

*.stackdump

# Folder config file

[Dd]esktop.ini

# Recycle Bin used on file shares

$RECYCLE.BIN/

# Windows Installer files

*.cab

*.msi

*.msix

*.msm

*.msp

# Windows shortcuts

*.lnk

Anyone has a suggestion what I could do to get rid of this issue?

Greetings David

D12294 · Jan 24, 2022

My problem was that LFS was missing from Git on the Mac laptop. After LFS was installed and activated the project was cloned correctly and the references were set. So this helped me:

1. Install homebrew from here https://brew.sh/index_de

2. Install git-lfs with homebrew

Code (CSharp):

brew update

brew install git-lfs

3. use git-lfs before clone

Code (CSharp):

git lfs install

git clone <clonepath>

bugcamper · Nov 7, 2022

I discovered a issue similar to this, but happen for a different reason: I started a thread here:
https://forum.unity.com/threads/nes...prefab-will-not-get-imported-refresh.1358405/

HernandoNJ · Jan 27, 2023

After moving the files to another path, the references were lost and there was a warning "Fix compile errors".
I solved the errors, the project recompiled and the references were recovered.

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Official Addressing issues with missing references

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