I have noticed that sometimes when I edit a post or someone else does it shows up at the bottom showing it was edited but sometimes it does not. More often it seems to not show up at the bottom that it was edited to me.
I’m not sure it’s a bug, it seems like the edit mark shows up when either someone edits their post after someone else has posted in that same thread or it shows up after a certain amount of time has passed before you edit the post. I’m not sure which it is, could be both, or it could just be a bug, don't know.