String instrument bpm bug?

So a few days ago I was playing a beat on the po-12 and had the op1 playing the String instrument with the endless sequencer. Both the op1 and the po-12 had the same bpm. 99% of the time both of them stay in sync (no cables are being used to sync the devices) as long as its the same bpm or multiple of it. For some reason though the string instrument wouldn’t stay in sync when playing on any of the sequencers. Other synth instruments on the op1 sync fine though. I think there is some type of bug with the String instrument. I restarted multiple times, made sure po-12 wasn’t on swing, double checked other things etc… Just wondering if anybody has had some similar issues with things not syncing with certain instruments on the op1.