This may be an instance-specific problem because I’ve had no problem editing posts on other instances. When I try to exit the title and body of this post, I click save (or whatever) and without error it behaves as if my change was accepted.
Most instances take a minute or two to re-render the screen to show my updates. If the wait is long, I sometimes do a hard refresh to make sure the change got accepted (and if I don’t do that and I do another update, the old content populates the form and causes the recent edit to be lost).
Anyway, with infosec.pub my edits on the above-mentioned post just take no effect, confirmed by a hard-refresh showing no change.
In fact the post I linked is not special. I just now tried to make a small edit to the post I am replying to, and it again had no effect.
Well, actually I was just now able to edit some titles of posts. So not all posts are treated equally. But note as well timing is irrelevant (I still cannot edit the post above).