If you look at the following screenshot you will see a bedroom on the left (assigned to a nyctophobic dupe) with two shine bugs, one elderly one nymph and neither are producing light, which happened when the nymph hatched as far as I can make out.
If you save at this point and reload, both start to produce light again, showing this is a bug, a shine bug...
So I include a save from just before the hatching. If you reload this and play until the hatching it is reproducible, both stop making light.
Curiously there is a cave top right with two more shine bugs in a similar situation one of which has also just hatched but they are still shining. One difference is that the cave bugs are not overcrowded when the bedroom bugs are. So the hatching occurred in an overcrowded bedroom. Another difference is the egg in the bedroom was moved by a dupe, by creating a sweep order for the egg to a sweep only compactor and then interrupting the dupe carrying it at the point it was intended to be dropped by giving them a move order, which caused them to drop the egg without adding it to a compactor (this happened twice with two different compactors, one now deconstructed, to adjust the egg location). FYI in case it is relevant.
Hope you can track down the bug.
If you reload this save and play until the bedrooms egg hatches it is reproducible, both stop making light.