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).

Further suggestions related to this topic:

You've got my vote sir!

Thank you for voting! Please offer suggestions or comments, if you think this could be improved.

As part of the Mr Handy Fix

Add New Room "Robotics Lab"

Each room holds 2 dwellers and 1 Mr Handy a 3x merged room can be assigned 6 Dwellers and 3 Mr Handies (This bypasses the one per floor limit however they are offline in maintenance pods cannot collect resources or respond to disasters (offline Mr. Handies will not take damage from disasters either))

Offline Mr Handies can be repaired over time at a rate dependent on the rooms upgraded level and the intelligence of any assigned dwellers

starting repairs will require a small amount of caps and junk but only a fraction of the cost for reviving a destroyed unit.

A fully upgraded robotics lab will allow you to upgrade an existing Mr Handy into a Mr Gutsy increasing HP and Effectiveness at managing disasters

(possibly allow crafting of other robots with different abilities and bonuses)?

What this does is provide a healing for any damaged Mr Handies as well as storage space for those that are not assigned a floor

Not sure the additional robot storage capacity is needed i doubt anyone will ever have 20 unassigned Mr Handies unless they are continuously cycling them into the wasteland.