I was playing Beat Saber and the controller was working fine, during the same play session, I went to play Population One and the controller desynced. I thought that the battery was low so I took it out and put another in it and the sync got even worse. I unpaired the controller, then I repaired, reset headset (not factory) and none of that worked. The controller cuts in and out of sync for a split second before it drifts away again. I do not know if it is something to do with the controller or the headset but I do not want to buy a new one. I have not abused or dropped it.
Your left controller is not syncing but your right one is the one not flashing the lights?. Shift your batteries around a bit in case it's a bad contact. Make sure your batteries are 1.5v. Not 1.2v. Factory resets are pretty quick overall and can do wonders. I heard SideQuest can backup many apps so you don't loose progress. I haven't looked into this problem much so I can't think of anything else.