@Arc that is not a checkpoint-specific option. Even if it is set, it should be ignored for checkpoint. Why would people playing co-op want humans on the opposite team?
I have disabled the option as a workaround, but clearly there is at least one bug here.
It was true; I have since changed it to false. I will reiterate that this shouldn't happen on checkpoint regardless of this setting since the game mode is checkpoint (co-op), not PVP.
I will also reiterate that with it set to true I could not select a class on the opposite team, so it seems there is a bug since you seem to be claiming that this setting
bAllowPlayerTeamSelect to true on checkpoint should allow team select.
IMO players should never be able to choose the enemy team in checkpoint.