When I add 9 files in my new project, timeline and the top menu, which is intended for changing the workspace, stop working. That issue appeared quite unexpectedly, I didn't update PrPro and any Adobe programs, services and plugins. Previous my big project worked without any problems.
I use version 15.2. Check out the bottom video. You can rewind the video to 1:00
Editing, Error or problem, Freeze or hang, Import, User interface or workspaces
So, that problem disappeared as suddenly as it first appeared. And I guess this issue will come back again in the future, and not only this problem. I very hope that Adobe will fix such technical issues very soon!