After drilling was performed, I noticed that the headphone would no longer turn on. Upon further inspection, one of the drill holes had penetrated leads in the circuit board.
Due to its physical damage, I was unable to perform a good diagnosis on the cause of the headphone issue. While not being an electronics engineer, my best guesses are either a processing chip or a capacitor malfunction (due to initially working but fading out, and functioning for longer periods if they haven't recently had a hard reset)
The physical damage prevented me from being as motivated to check for signs of component failure, especially knowing that this pair of headphones was likely irreparable at this point.