Bug Prefabs Missing when upgrading from 2018.3 to 2019.4

For some reason when upgrading from 2018.3 to 2019.4 I get tons of prefabs missing like described here Bug - REGRESSION: assets that failed to import result in missing prefab that lose the original name - Unity Forum

I also get compile errors due to some plugins that need to be updated after the engine upgrade, once these errors are solved prefabs are still missing even If I reimport all or delete the Library folder.

Ive spent quite some time trying to fix this and I found that the .meta files of the scene where the prefab is missing is 100% the same as the one in 2018.3 with a valid guid reference to the prefab. If I delete the missing prefab and drag and drop the prefab again then the .meta file changes, see below:

Prefab .meta (truncated for better visibility):

Code (CSharp):

1. fileFormatVersion: 2
2. guid: 1dfe7b28f313a8844b1cb402b2739ed3
3. ScriptedImporter:
4.   fileIDToRecycleName:
5.     100000: _MapPrfab/harbour
6.     100002: _MapPrfab/harbour/Grid
7.     100004: _MapPrfab/harbour/Grid/Bridges/Walls/Trees/Darkness/Waterfalls
8.     100006: _MapPrfab/harbour/Grid/Bridges/Walls/Trees/Darkness/Waterfalls/Chunk (16,32)
9.     100008: _MapPrfab/harbour/Grid/Bridges/Walls/Trees/Darkness/Waterfalls/Chunk (32,0)
10.     100010: _MapPrfab/harbour/Grid/Bridges/Walls/Trees/Darkness/Waterfalls/Chunk (32,16)
11.     100012: _MapPrfab/harbour/Grid/Bridges/Walls/Trees/Darkness/Waterfalls/Chunk (32,32)
12.     100014: _MapPrfab/harbour/Grid/Bridges/Walls/Trees/Darkness/Waterfalls/Chunk (48,0)
13.     100016: _MapPrfab/harbour/Grid/Bridges/Walls/Trees/Darkness/Waterfalls/Chunk (48,16)
14.     100018: _MapPrfab/harbour/Grid/Bridges/Walls/Trees/Darkness/Waterfalls/Chunk (48,32)
15.     100020: _MapPrfab/harbour/Grid/Bridges/Walls/Trees/Darkness/Waterfalls/Chunk (48,48)
16.     100022: _MapPrfab/harbour/Grid/Bridges/Walls/Trees/Darkness/Waterfalls/Chunk (64,0)
17.     100024: _MapPrfab/harbour/Grid/Bridges/Walls/Trees/Darkness/Waterfalls/Chunk (64,16)
18.     100026: _MapPrfab/harbour/Grid/Bridges/Walls/Trees/Darkness/Waterfalls/Chunk (64,32)
19.     100028: _MapPrfab/harbour/Grid/Bridges/Walls/Trees/Darkness/Waterfalls/Chunk (64,48)

With missing prefab 2019.4 (notice guid: 1dfe7b28f313a8844b1cb402b2739ed3 is correct but fileID seems to reference childs of the prefab, eg: 100000,400000,etc

Code (CSharp):

1. --- !u!1001 &1915161834
2. PrefabInstance:
3.   m_ObjectHideFlags: 0
4.   serializedVersion: 2
5.   m_Modification:
6.     m_TransformParent: {fileID: 1821289052}
7.     m_Modifications:
8.     - target: {fileID: 100000, guid: 1dfe7b28f313a8844b1cb402b2739ed3, type: 3}
9.       propertyPath: m_Name
10.       value: harbour
11.       objectReference: {fileID: 0}
12.     - target: {fileID: 100000, guid: 1dfe7b28f313a8844b1cb402b2739ed3, type: 3}
13.       propertyPath: m_IsActive
14.       value: 1
15.       objectReference: {fileID: 0}
16.     - target: {fileID: 400000, guid: 1dfe7b28f313a8844b1cb402b2739ed3, type: 3}
17.       propertyPath: m_LocalPosition.x
18.       value: 0
19.       objectReference: {fileID: 0}
20.     - target: {fileID: 400000, guid: 1dfe7b28f313a8844b1cb402b2739ed3, type: 3}
21.       propertyPath: m_LocalPosition.y
22.       value: 0

Now, after I delete the bugged missing prefab and re-drag and drop the original one into the scene, notice FileID is now a negrative big number:

Code (CSharp):

1. PrefabInstance:
2.   m_ObjectHideFlags: 0
3.   serializedVersion: 2
4.   m_Modification:
5.     m_TransformParent: {fileID: 1821289052}
6.     m_Modifications:
7.     - target: {fileID: -8754723954883928660, guid: 1dfe7b28f313a8844b1cb402b2739ed3,
8.         type: 3}
9.       propertyPath: m_Name
10.       value: harbour
11.       objectReference: {fileID: 0}
12.     - target: {fileID: -8646016225646303417, guid: 1dfe7b28f313a8844b1cb402b2739ed3,
13.         type: 3}
14.       propertyPath: m_RootOrder
15.       value: 0
16.       objectReference: {fileID: 0}
17.     - target: {fileID: -8646016225646303417, guid: 1dfe7b28f313a8844b1cb402b2739ed3,
18.         type: 3}
19.       propertyPath: m_LocalPosition.x
20.       value: 0
21.       objectReference: {fileID: 0}
22.     - target: {fileID: -8646016225646303417, guid: 1dfe7b28f313a8844b1cb402b2739ed3,
23.         type: 3}
24.       propertyPath: m_LocalPosition.y
25.       value: 0
26.       objectReference: {fileID: 0}

It seems like .meta was not migrated during the engine upgrade, possibly due to a compile error

What is the recommended procedure to follow now?

Thanks

 

This is exactly what I did, but I still end up with these broken prefabs

What I did was created a copy of the project in 2018.3 upgraded it to 2019.4, fixed all the compilation issues and then pasted those fixes in a fresh copy of the 2018.3 one, opened the project in 2019.4 and upgrade. I had 0 compilation issues but still a bunch of broken prefabs

Should I attempt 2020.x ?

 

Here I managed to recreate the issue:

• Open the scene in SuperTiled2Unity->Examples->Overhead in 2018.3.12.f1
• Confirm TestOverhead is seen and close the project
• Open the same project in 2019.4.17f1

Reimporting won't fix the problem nor anything else I tried above

Project: https://we.tl/t-kd2FfFsxYb

Edit: The same happens from 2018.3.12.f1 to 2020.2 - reported bug under 1303493

 

The same issue happens if you upgrade from 2018.4LTS to 2019+

 

FWIW I'm the author of the SuperTiled2Unity plugin and I've been able to reproduce the bug @Alkanov mentions. I've spent some time trying to diagnose but no luck so far. If anyone from Unity has some advice I'm all ears.

 

@SteenLund @Alkanov Did either of you ever figure out how to fix this? Experiencing a very similar thing.

 

Is there any update on this? I'm migrating an old production project from 2018 to 2019, and It's happening the same. No matter if I migrate to 2019 or 2020, prefabs go missing. What's the correct approach? Reimporting doesn't seem to fix the issue.

@SteenLund @Alkanov