I suddenly recognized that the small icons in the upper right corner were gone!
Now it is impossible to restore, minimize or close After Effects without using the main text menu and close the whole project!
I have tried all the common ways to reset the Workspace but these little icons is still missing!
If anyone of you guys know how to fix this I would be pleased to find a solution with your help!
Nobody can tell you anything without proper system info or other technical details.
Trash your AE Prefernces file.