I'm making this thread to bring visibility to this bug and possibly to find other people with the same issue. I tried updating my 2017.1.1 project to 2017.2f1 and while the update itself went smoothly, I've encountered a fatal editor bug that is preventing me from upgrading. Basically after opening my project in 2017.2 and pressing play the editor might freeze and lock up, requiring me to close the editor from task manager. This happens before any of the scene scripts are being run so it can't be an infinite loop or other script error. The editor does not go to the "Not Responding" state; it just doesn't accept any user interaction. The weird part is some completely arbitrary actions in the editor before pressing play may fix the problem so the editor doesn't lock up and starts normally when pressing play. Some of the actions I've found to do this are: - Simply clicking on some objects in scene hierarchy before pressing play - Changing random settings from project settings, specifically changing asset serialization to "force text" (however the issue is back on the next editor launch even with the changed settings) The issue might also come back after few minutes so doing these "fixes" once isn't a solution. I have not been able to reproduce this in a dummy scene so I can't file a bug report. The issue does not happen in an empty scene, but I have not been able to isolate any certain object causing this behavior either. I'm also not comfortable sending my 20gb project to Unity so I'm kinda out of options. So few questions: - Anyone else noticed this? Maybe even a known issue? - Are there any ways for me to debug this? Like I said I can't isolate the issue to a certain script or object, and the issue happens before any of the scene scripts are even ran.