No idea why this is marked as "Solved", because I can't find a solution here
Anyway, I can't talk to our host, because I got the server running on a dedicated machine. It works perfectly fine on my PC when I host it locally, but the AppID always pops up when I start the server on the dedicated machine.
This does not seem to cause any issues while playing or so, at least not that I have noticed, it's just weird.