We sincerely apologize for this launch issue and appreciate you sticking with us through it. We believe we have found the cause of the bug where you join a match, spawn, and are killed by the fog.
If you joined a server that was still in the lobby que you would spawn okay, but if the match had already started, our server backend was failing to close the matchmaking que which would allow players to join in and then die instantly.
In our internal testing this seems to be fixed. If anyone continues to experience this after getting the latest update on Steam please let us know right away.