I’m aware of that bug, but the bug is in FVTT unfortunately, so not much I can do about it. It happens if you launch the server with the --world option and if you try to accept it shortly after it started.
The only way to prevent this would be to force a delay after the server starts before I give access to it, but I don’t want to do that as it will delay the first launch of everyone even when it’s not necessary, and I like that it launches the game as quickly as possible and seamlessly.
I reported the issue to Foundry and they said it should be fixed in the next release.
I guess I can just add the delay now temporarily until 0.5.2 is released.