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Is there any direct input to the KRK10S subwoofer? as opposed to using a wireless or Bluetooth input to it?
If so, trying to use one such direct input, to test it, would be ideal at this point... the result would tell us whether the problem is one type, the other type, or another problem.
So the sub itself appears to either be muted, or to have a defective speaker and/or amplifier to that speaker inside the KRK sub, or else its volume control is turned all the way down... or else, just perhaps, the selection of the input is still on the Bluetooth, but not on the direct line going into it.
Which of these sounds most likely? I think the defective speaker or immediate amplifier for that speaker. But check the volume control, and the input selection (if applicable.)
Which light is that, please? does it have a label next to it?
Red means a bad status for sure, if it usually is green when it's working.
Have you tried any kind of reset of the sub? how long has it been having this problem, please?
Unplugging it - from everything - and leaving it off for 20+ minutes would be a start. (But with a problem of a month's duration, that's probably already been done.)
There may be another reset - I am looking for it....