This issue seems to only affect the Windows 10 version and I have seen it happening to other people. As described in the summary, if you unfocus the game in any way (clicking off of it, minimizing it, or alt-tabbing) then when you click back onto it, if you're on a server, you get kicked out and can't rejoin that server or any other server until you restart the game.

Steps to reproduce:

1. Join a server
2. Unfocus the game in any way
3. Refocus it
4. You're kicked out and can't rejoin