I was playing Fallout Shelter when a random Rad-Roach infestation happened. When a roach went to a room and glitched.Suddenly, All the roaches were invincible. I had two Vault Dwellers that had Max Endurance Firing at one with Gauss Rifles against one and it killed both of my dwellers, Then is spread out all across my vault and killed /everyone/ except a few in a safe room.

Ya I have noticed this happens with molerats too. Its interesting because even after they kill everyone in the room they still just stand there with the attack animation for about 20-30 seconds before freeing up.

Something to keep in mind: if the room that an incident is in has been upgraded, the incident in that room is also upgraded.

For example: 6 people in a Diner can be somewhat low level with basic weapons and do fine, but those same people in a Restaurant would almost die, even at level 15, and in a Cafeteria (max level room) would certainly die unless you keep them healed.