Have had this happen a few times now. Ion running 2.6.1 with universal fader wings.
When unloading subs or other content mapped to faders, the fader LED remains on.
Have tried using [shift] + both buttons, then [delete] + fader number. It appears cleared and functions as normal in fader config, but the LED stays on.
The only way I've found to clear it is to load something else on the fader and then clear it again, which only works sometimes. It seems to have no real effect on operations other than being mildly annoying. It also happens more often when loading pre-2.6.1 show files.