Broken project: either doesn't load, or builds EVERYTHING PINK

My main project of mine has just broken and I have absolutely zero clue why.

First it just failed to load at all: as soon as I selected it from the load screen, just nothing happened: no "this is loading, this is updating" little window: nothing at all.

After many useless tries, including re-downloading the project from scratch, I re-installed the Unity Editor.

After re-installing, the project loaded, and it worked in-editor. But in builds, everything was pink. Just a pink screen and that's it. No sound. However behind the pinkness, I think the game was still somewhat responsive. Difficult to say, since it was just pink.

Re-importing the assets did nothing.

Now it again completely fails to load, and that's it.

Editor-prev.log ends like this:

----- Total AssetImport time: 0.081435s, AssetImport time: 0.048692s, Asset hashing: 0.000000s [0 B, 0.000000 mb/s]

Refresh: detecting if any assets need to be imported or removed ... Refresh: elapses 0.010171 seconds (Nothing changed)
Cleanup mono
debugger-agent: Unable to listen on 63
[usbmuxd] Stop listen thread
[usbmuxd] Error:
[usbmuxd] Listen thread exiting
Callback unregistration failed. Callback not registered.

(Filename: /Users/builduser/buildslave/unity/build/Runtime/Core/Callbacks/CallbackArray.h Line: 192)

Checking for leaked weakptr:
Found no leaked weakptrs.
##utp:{"type":"MemoryLeaks","allocatedMemory":1376634,"memoryLabels":[{"Default":3988},{"Permanent":16768},{"Thread":648},{"Manager":2704},{"VertexData":11376},{"Texture":96},{"Shader":293760},{"TextureCache":-96},{"Physics":8},{"Serialization":15712},{"JobScheduler":144},{"BaseObject":5484},{"Terrain":224},{"STL":8192},{"String":99140},{"DynamicArray":20044},{"Curl":176},{"PoolAlloc":-224},{"ScriptManager":13080},{"Sprites":659912},{"CloudService":296},{"WebRequest":7444},{"VR":7796},{"EditorGui":332},{"EditorUtility":544},{"AssetImporter":2432},{"RestService":64},{"License":574},{"UnityConnect":9232},{"WebViewCallback":6192},{"Collab":190592}]}

Editor.log ends like this instead:

Loading native library: UnityEditor.iOS.Native at /Applications/Unity 2017.1.0/PlaybackEngines/iOSSupport/UnityEditor.iOS.Native.dylib
[usbmuxd] Start listen thread
[usbmuxd] Listen thread started
[usbmuxd] Send listen message
Native extension for iOS target not found
Native extension for Android target not found
Begin MonoManager ReloadAssembly
Shutting down Remote Indexer
Task failed: Downloader Task
Cancelling tasks, domain is going down

I'm using 2017.1.1.

I also tried with 2017.1.0 but nothing relevant changes: I select the project, I get (as expected) the "non matching editor window", and as soon as I hit "continue" it just hangs.

=== Update 1 ===

I've read someone suggesting to start offline. Indeed when I tried to work offline the project started.
I don't know if that is the reason, but it's pretty odd if it is, since it happens only with that project.

=== Update 2 ===

When it does work (i.e. it's pink, instead of just not starting), I get these logs among the others:

<i>OSXPlayer(Gnaw)</i> Unsupported: 'Hidden/VideoDecodeOSX' - Pass 'FLIP_RGBARECT_TO_RGBA' has no vertex shader

<i>OSXPlayer(Gnaw)</i> Unsupported: 'Hidden/VideoDecodeOSX' - Setting to default shader.

Obviously zero clue what they are talking about: I don't do shaders, and I certainly didn't modify anything related to them today.

=== === === ===

I am completely clueless about what to do now, I'm stuck and I can't work any more.

 

In a test scene I got this:



Seriously, what's going on?!?

 

This comment finally solved it.

Why I had this problem also when re-downloading the project from scratch, I still have zero clue.