I've had three instances of issues with the final wave with the boss buging out with two different versions of it. The version of the bug I've had twice is that the rewards chest doesn't spawn after the boss is dead. I think it might be something with the wave's augment spawning in the same rough time as the boss dies as the enemies from it persist. IE, we kill the boss as the Sparkholder enemy spawns in and it persists after the boss and you can do it's whole bit. Same deal with the shielded enemies that need you to grab the Darkness Empowered buffed before stripping their shield and killing them. Never found a way to get the chest to spawn so the whole run turned out to be a waste. The version of the bug that I've had once, just now actually, is that opening the door to the area just spawns nothing. Empty room, no boss, no nothing. Not sure if there's some check between people rallying at the banner and and shooting the nodes to open the door or something but couldn't get anything to spawn in, so the run turned out to also be a waste. When you have this happen in back to back runs, it gets kind of annoying when the last 30ish minutes basically amounted to nothing.