Acrobat DC is loosing windows title bar

i experts,

I was migrating to Acrobat DC Pro which runs under Windows 10 X64

My Problem is:

In many cases Acrobat DC looses the windows title bar.

I then have to press F9 to make the title bar visible again.

This happens not only when starting Acrobat, but also while working with a PDF.

How can I solve that problem ?

THX for any help.

Tom