No script asset for GameObjectSelectionItem. Check that the definition is in a file of the same name.

After updating to the latest Unity version I’m receiving this issue sometimes while test playing the game. It’s not always but happens randomly most recently when I’m clicking a button transitioning to another scene. But had it happen earlier when I worked with cloth too. Anyone know how to fix it?

Is your Animation window open? That caused the bug for me and it went away after I closed it.

I’m having the same problem. Unity 2018.1.0f2 Personal (64bit)

I figured out what it was, I had disabled the fade in effect while test playing some scene. The script couldn’t run the animation so got that error. On the earlier versions that didn’t seem to be an issue it kept playing without the UI element being animated. You just got to enable the UI element that you’ve animated while test playing.