Randomly kicked to main menu

While waiting for the match to start (it was like 1 sec before spawn door opening) I got kicked to main menu. There was an option “Rejoin match” which refused to be clicked no matter how much I tried. After some time passed while I was unable to do anything - I decided to restart the client. Came back to a 15 min ban.
WTF was that?

Your computer wasn’t able to complete the connection to the server where the match was being hosted. The match was working for the other players, so the disconnection counts as a leaver penalty. You can read more about it in the pinned thread:

Usually when connection drops I see low-poly splash screen with a spinner “Entering game”. But no, I was dropped into main menu, as if I have a connection. I saw “Rejoin match” option, so the client was aware I should’ve been in the match, but nothing worked nonetheless.

Yes, it was aware, but the server wasn’t able to reach your PC to complete a connection. That’s why the WinMTR is used for diagnosing the issue.