UPDATE
I’ve narrowed the problem down a little more. It’s only when loop mode is turned on.
Leaving the track running maintains perfect sync. Turning on a short loop causes the tempo to drift. This suggests that the BPM is fine, but it’s that the loop isn’t repeating exactly on the bar mark as it should (so just a fraction before the end).
I’ve tried changing where the loop start and end markers are placed but there’s still the drifting problem. They appear to snap perfectly to the bar start and end points as they should.
This is fine for a 32 bar loop as it’s just the very end (or the very start) that’s causing a problem. With say a 4 bar loop though, the drifting’s pretty bad.
Can anyone else confirm this?