[Welsh Anorak]

Keep an eye on the tape counter. If it stops while the tape is playing normally you have a problem with the reel rotation sensor - very often a clean is all that's necessary. Most mechanical problems with tape rotation tend to happen either at the beginning of the tape when the speed is too slow to spool the tape or towards the end when the weight of the full spool slows the mechanism down. Your random timing suggests we may have a sensor fault. Or maybe not!
Glyn