I hate how the bosses spawn in dumb spots like on sanctum when one of the mantises spawns in the armory and you cannot shoot it or anything.
and i always lose on the last round because of this
I also dislike how far away you’ll respawn from the current round objectives. 
It already takes so long to respawn on the later rounds, but then you have to add the time it takes to run all the way back.
Definitely awful respawns. Once I had to kill 4 promethean knights and all of them were inside the garage