I've made a topic about this before but it still happens and I'm slightly sick of it.
If I am hosting and my brother does something on Blockland (not sure what causes it exactly... joining a server? Querying master server?), everyone in my server leaves. I get a bunch of "Client ____ timed out" in the console. My authentication still works fine.
I can't seem to get the server back up after he quits, either.
We run off the same wireless router, and we have different keys.