Basically as per the title. It doesn't appear to be a wiring issue, as I've measured DC resistance with a multimeter directly on the driver terminals - the working driver is ~240 ohm while the other varies from 8000 to 10000 ohms. The issue occurred spontaneously while listening at low volume.
Interestingly when hit with the full force of the O2 amp, it sounds completely perfect, just extremely quiet - about 5% the volume of before.
Has anyone experienced this before and is there anything I can do to repair it?