it happened to me a couple of times a well. It's quite annoying when you have a nice run with your future to be friends (aka strangers) and you get spawn somewhere else. I haven't seen it happen before too. It seems to be a new 'feature' since last week.

It happened in lower map as well with my alt (lvl5) we got split into 2 groups. I already sent a friend request, so i could join the group again after the system dumped me in another game. Therefore i would say it is not only in slouch-o maps.