I just played an Execution match in which the enemy team had 8 players, and our team had 6. All Execution lobbies are supposed to be up to 7v7 as far as I know, which means there’s a 14 player cap, which means no one was going to join to even out the teams (and none of the enemy were willing to switch, of course).
I don’t know exactly how this bug came to be, but I know it was set to 8v6 in the lobby before the game began, so no one used any illicit team-switching to make it that way, or so it seems. That’s really all the information I have, and this screenshot.