My buddies and I were noticing that we are sometimes getting left out of a wave spawn, despite being active (not afk) and simply waiting in spectator mode after a death.
It happens infrequently, but enough to be quite annoying. It also seems tied to menu actions, whether that be hitting escape, in your load-out menu, you will not spawn with the rest of the team.
We have remedied this by making sure not to press anything just before wave spawn--not an ideal solution.
Anyways, I hope that made some sense.