I've come back to my game now after a half hour. Everything seems fine - enough food, water and electricity.
But as I selected the first person to check their health, he was radiated about the half of their life. I checked all others. EVERYONE is radiated. What could happened? I have 40 dwellers in many different rooms. Is this a bug or was there another fallout? :-D
I found the reason as it happened again. My water reserve was on the edge of minimum which looks green but was too low for my dwellers. They get radiated. The radiation faded away after getting enough water for longer time.
I think while you were gone there was maybe mole rat ora rad roach infestation and one of your dwellers got poisoned. Like real-life poison spread. According to the fallout, it was radiation. With enough rad aways, or clean water, your all good until. But my method is to have 6 people working in a maxed Science lab. all with outfits that greatly increase inelegance. (lab coats) With patience, it's a good method.
When you log out your vault is still using recourses for some time. Possibly you had just over the min needed water and when you left the water went under the minimum giving all the dwellers radiation. Then when you logged back on you collected more water so you had over the minimum amount so it appeared ok but they had been collecting radiation for a while.
I think I know what might have happened.
In fallout shelter, if you bring a radiated person in from the wastelands, the radiation can spread. To see if your person has radiation damage, look at their Heath bar. If they do have it, there should be a bit of red in it. Make sure that if your dwellers Heath is a bit red when they get back, give them a radaway.
Hope I helped.
