During combat Dwellers are stacking, and sometimes the health bar doesn't show. If both of these happen simultaneously, you will usually have casualties. I have stopped playing Survival Mode until this issue is resolved. A combat system that is critically flawed takes away from an otherwise decent game. Tilting the screen: This is barely a viable option, as it is simply too unreliable, especially with a multi-stack of three or more (when full 3D is on).
My suggestions on this topic:
Mr. Handy should have more toggle options; Collect (Y/N), Combat (Y/N), Firefighter (Y/N).
Mr. Handy should have an inventory to hold 10 each of Stimpaks/Radaways, creating another toggle option; Medic (Y/N) (There is plenty of room on the Mr. Handy pop-up to add these options.)
Mr. Handy should have ghosting ability, making it impossible to select him while he is in a room during combat. (If you've already toggled Combat (N), he will flee on his own.)
The health bar for Dwellers should ALWAYS be present during combat; within any room containing enemies or fire, until the threat is eliminated.
No dweller stacking during combat; essentially the same as fire events are now (I've never had a dweller stack during a fire).