In playing Boss Rush so far I have had happen:
-Challenger Prime completely not triggering: In instances where I still have the prime available it is just not going off at all(has happened to myself, multiple times)
-Zombie State: After Challenger prime triggers you enter a pseudo alive state, burning challenger prime. To others my character is alive and shooting with rez visuals and orange overlay active. I can shoot, but my UI is gone. I normally die within 1-2 seconds to no apparent cause. Character can be interacted with and rezzed by allies, and will resume normal functions.(Has happened to both myself and others, multiple times)
-Incorrect health trigger: While at 25% health visually remaining, I have entered the challenger rez animation. Instead of going from 0% to 100% health, I go from 25% health to 100% health.(Has happened to myself multiple times)
-In a likely related vein, individuals using handler as their primary have been observed dying immediately to non-execution attacks(ie Shahala lazers) while not having used handler revive, having relics available to fuel it, and both allies having relics remaining to revive. (Has been observed a single time)
All bugs observed were in duo or trio Boss Rush Gauntlet Apoc, and generally confirmed by others in the group