@mayel @ivan Wow this was a tough one to find.
It's happening in the smaller post composer that pops up on the bottom right of the screen. Using a Mac, Google Chrome, 1700px or wider screen.
So for some reason when I reply, the Content Warning is being enabled by default. If I KEEP it enabled, then the space on this smaller posting window isn't being recalculated (minus content warning box space), and when I get to the end of the box, it runs over and I can't view what I'm typing.
So I had figured I had hit a "hard stop" and it wasn't allowing any further entry. I tried two different themes and it happened on both. Happened on three different themes, so no theme specific.
Removing the content warning option fixes the issue. Hope this helps. I've noticed some great speed improvements lately, by the way!
Attached video (maybe?). 😊