gritty sparrow
Sometimes when I'm tinkering with the lights, I either edit the color, or split them from a group, or something like that. The light then turns completely black and won't illuminate, and I can't seem to find a setting to disable it, even undoing and redoing doesn't seem to fix it.
sharp marsh
If your time isn't paused and you are doing this during the day the lights automatically turn off. If you want them back on switch to nighttime and pause time. Then you can switch to day and they should stay on.