I’m also having this issue - I’ve learned to export a copy of the bestiary every time I add a monster to it, which works but does mean that if I miss doing that, I’m out work. Even saving it in another location doesn’t seem to help.
That seems to be a very unsatisfying process! What version of the DM Helper are you using? Could you join our Discord server? Then we could chat through how to find a good solution for you.
I just went to check that it was still happening and the monster I created stuck around, so whatever was causing the issue seems to have fixed itself. I did run a bunch of updates on things recently so maybe something there caused an issue. All good now!
