Beastmen spawns seem to still be really buggy and spawn on top of players a lot. I can’t say for certain obviously, but every time I see this happen nowadays it is always Beastmen, although I have read people saying they experienced it with Skaven and Chaos, just with no video proof.
Happens with other races too, and surprisingly often. There really should be an area around the player where nothing can ever spawn, LoS or not.
Looks like spawns trigger ‘on’ a certain player, and doesn’t take into account proximity or LoS of other players. Also most of the time that happens, it would still be too close to the player they’re spawning on, as well.