Nothing has happened to them. This system ensures that all of those inmates are maintained in optimal health. But they have left the dome -- this dome. The code that maintains the dome as you see it requires constant alteration, and occasionally, errors are introduced that cannot be fixed in a timely fashion. When that happens... for affected inmates, it is like falling asleep.
They disappear from this dome, but they are still sleeping in the dome where you were last night. In due time, the error will be corrected, and they will wake up again and be returned to this dome with the rest of you.