Sudden volume drop TU-8600S (TKD 2CP601S)

I was using my amp today, and after about 6 hours, suddenly the volume dropped to a very low level. I turned down the volume, switched off the amp, and a few minutes later I turned the amp back on, turned up the volume and everything went back to normal with the volume. I am not sure why it happened. I usually use my amp 6-8 hours at a time. Has anyone else had this issue?