It doesnt happen when there are no humans! My server is 32 slots, 16vs16, when theres no humans all 16 bots are nicely spawn and scoreboard gives all 16 playing with their scores correct
When I join and specced the bots spawning (keeping scoreboard key pressed), i see they all go for A SPLIT SECOND in spectatormode and then join team. Usually one stays stuck in spec mode , sometimes there's more