Is there a limit to the number of enemies spawned during the timed waves of the Mass Effect 3 multiplayer?

I can only speak for Bronze rankings. For this type of mission depending on which wave it is you will get stronger monsters that spawn plus the trash monsters. After the stronger monsters are dead, the trash monsters will never stop spawning, they will also continue to spawn in the same area until your team moves to a different area or completes one of the 4 disarmings.

I have done this a few times with reapers as an enemy, I forgot which wave, but there was 2 banshees and 2 brutes and 3 or 4 ravagers. After all those enemies were dead the only monsters that continued to spawn were cannibals and maruder and rarely a few husks would come running.

I forgot the numbers now and dont have it in front of me at work, but I think 8 enemies can spawn at once and only a maxium of 2 spawn points at a time. So from what I have seen, no facts behind this. So if you know where current spawn point is you can run the backways around the map as they head to your last location (as long as you dont shoot) and than can get the next objective and never have to shoot at the trash, and until you kill the trash more wont spawn.

But I have stood in the same spot for 4 minutes with a sniper rifle and let them run down the hallway and killed 20-30 monsters in the 4 minutes because spawn point didnt change because I did not move. 4 minutes ended, my mission ended, but got like 20k score.

They do replenish. Not only that but they seem to replenish the same enemies, so if you kill four atlases, four more atlases respawn (waste of time). Weaker enemies (or tough enemies that have you pinned down), it's a good idea to clear one wave and then move to the objective. If they are spawning between you and the objective, forget about it, just run for it. Generally a good idea to flank safely around them though: while you're doing so the respawns may shift to a more manageable location.

Fighting Reapers on Silver, 4 Banshees spawned in succession, after the four banshees were dead none spawned for the remaining minutes or so. The mooks kept respawning but none of the mini boss types.