1. What happened?

Still getting more information, but for some users, after pulling the latest changes in their project via Collab they see the "Check workspace has not changed" message appear. After the message appears, the progress bar freezes and freezes the rest of the Editor.

The workaround so far has been to selectively save out local changes, restoring to an earlier commit, then trying to update to the latest revision. Afterwards, the copied out local changes can be pasted back in. In addition to that option, the project can be re-downloaded from the Cloud using the Launcher and allow them to continue working, minus their most recent local changes.

2. How to reproduce this issue?
Still collecting data. Need more user reports with logging enabled, -enableCollabEventLogs.

https://forum.unity.com/threads/solved-collaborate-freeze-unity-unity5-6p2.468150/#post-3296104