I have been posting my struggles with tape loops midi drift using the OP-1 as slave. I have resolved these issues and thought I would share with the community so that others do not suffer the same headache.
If you want pre-recorded tape loops to play in sync to external clock, you must record the tape with the OP-1 usb UNPLUGGED. There is something going on with the internal clock and laying down new tape tracks when plugged into usb where no matter what metronome mode you are in- EXT sync or Beat Match- it will drift from your external gear. Tape tracks recorded with the OP-1 unplugged from any USB sync and the tape syncs perfectly.