invalid dist DEDICATED_SERVER when spawning my mob

I made a very simple mob that for now doesn't have any special properties, and in singleplayer this works perfectly. But when I put it on a dedicated server, it gives me this error.

https://pastebin.com/4g78cu6Y

The server does launch, but every time the mob should spawn - no matter if naturally or through a spawn egg - the server shows this error instead.
I don't know whether this is a bug or not, but I can't find a solution for this anywhere, so I decided to post it here. I'd be glad if anyone could tell me a fix for this.