thank you for the now useful answer!
I did not had it before in Windows 10, not in the normal build (Home & Professionell) and not in any Insider Previews before this one, very strange.
I found the post you mention too but that is already a few months old (and it seems to be fixed), that is the reason why i made a new one, this Insider Preview is only a few days old.
To explain the problem a little bit more:
Every few seconds the menue-bar (File, Edit, etc.), the toolbar below the menue bar and the bar at the bottom of the window starts flickering for a few seconds and the program is not responding. The size of the window does not has any influence on that behaviour. All other windows from HeidiSQL (Session Manager, etc) are not affected, only the main window. I think it has to do with some UI-redraw, when i switch to other open programs some of them are flickering then too. But when i close HeidiSQL all others are fine all the time, so it seems that it is coming from HeidiSQL. The MySQL Server i connect to is a 5.6.21 from AWS connected over TCP/IP. The HeidiSQL version is 22.214.171.12478 (i tried it with the latest nightliy build). The screen resolution is 1920x1080, so nothing fancy with high DPI there.
I hope this helps,