Sync OP-Z with Volca keys

Can anyone advise please…
I’d like to sync my OP-Z with my volca keys.
I have an OPlab in my OP-Z.
I have cable going from sync port in op lab (OUT/MIDI/PO) to sync in on the volca keys.
Everything seems good between the two (the clicks are in time and change in sync as I change the speed). However after about thirty seconds the volca seems to skip a beat and continue with a skipped beat.

Any suggestions as to what’s going on?

Thank you.