10
... this happens more often on cursed memes. /s
I can still slide to open the menu, but cannot take action on the feed. (The + button opens in the fore-foreground, so it works as well as 'back to exit' Connect.)
I was playing with the thumbnail preview in fairly rapid succession when one just "stuck".
Just got it.
It's tap and hold thumbnail with one finger -> use another finger to do a "zoom out" gesture on the screen.
It seems to happen only on image posts, and when you don't trigger a page reload or side menu open behind the opened preview.
(Also, it's still super rare to trigger the bug. I only just got it twice since I started responding to your comment.)
Edit: Reliable trigger:
Press and hold thumbnail -> use another finger open side menu -> click "All" or other menu choice -> release first finger.