Fallout Shelter possible bug?

So when I was playing this morning I opened my iPad to a nice healthy vault, full resources still, etc etc. only issue was I noticed my happiness was low compared to when I left.

After 5 mins everyone in my Diner and Water Treatment room died. All at once. Everyone else was fine and any pregnant women in the rooms were fine too. My food, water, and power were not only full when i signed in but I collected things after signing on too so I had a major surplus. The only hint anything was wrong was these people had happiness levels in the 20's.

My brother had this issue as well whilst playing, he didnt sign off or close his ipad for a few hours it just happened as he was playing. Peoples hp began dropping like a select few of them were refusing to eat and began to starve while everyone else in the other rooms remained untouched hp wise.

Has anyone else encountered this and if so do you have any clue what it is? Are there diseases? Invisible untraceable rad sickness? I had people out exploring, I cant help but think the damage meant for my explorer somehow transferred to other dwellers. The explorer is a lvl 40 legendary so I could see how things he could survive would murder normal dwellers in seconds.