Never seen a bug like this.. What I would suggest is force hibernating your server, activating it, then turning it offline. Then click Reset World, wait for it to load, then start the server back up again.
Also make sure the world in Level Name under the category Settings is the one you want to reset. If all else fails, just go into File Manager go into Deletion Mode, select your world, and delete it. But be aware this will delete all player data for that world too.