Feeling dumb because it took me so long to figure this out, but smart because it’s an important discovery.
Somehow, several of my AZ login sessions have happened to expire right in the middle of writing a post, causing the Submit button to malfunction, with no clue/indication about what failed or why.
I have managed to log in, refresh the screen that had my post still written, and then successfully submit the post. Most members would probably lose their work when they ran into this problem.
I suspect this is a problem that @unseen also ran into fairly often, and none of us could explain what was going wrong and how to work around the problem.
I’ve detailed the workaround in a Tips group topic (in italics) but most members probably won’t find it (except by accident), and the workaround itself is easy to flub.