This is embarrassing unity... I've had to completely remove my project and re-clone it from git to get rid of these issues.

It happens after I import Google Play Games Services plugin. My platform is iOS. I cannot continue my development because each time I press Play, Unity crashes...

We are still experiencing this in Unity 5.4.1f1, causes serious workflow issues. Please fix : )

Everyone on the team gets this from time to time, our entire project gets screwed up, then we wind up needing to delete library and relaunch (currently takes over an hour to complete since our project is so big). Multiplied by the size of the team this is costing serious $$$$.

Get this every day, has been like this for years now.

Unluckily, I'm on the same boat like you guys. I'm still onUnity 5.0.1f1 and as I can see it doesn't make sense to update. That's really bad.

I have to close Unity, move the content from Data\UnityExtensions extensions folder to a temp place, open Unity, close Unity, move the content back back, open Unity.
The work around lasts until it breaks again...

5.4.0p3

Happens for us regularly when doing asset bundle builds via BuildPipeline.BuildAssetBundles (ie, Unity5 asset bundle build).

Means we are stuck using our old U4 build system until the issue is fixed - we can't afford the reimport times as our projects are very large.

Still in 5.4.0f2

This issue occurs too frequently and costs my employees 2 hrs reimport time because the project is so large. Please give this some attention.