ATEM 4 M/E Constellation 4K -- Timecodes not matching

Two Micro Studios connected to an ATEM 4 M/E Constellation 4K, with an Mini Sync generator plugged into REF IN and genlock set to Program in each camera. Testing genlock with a sync slate and I'm observing a 1 frame discrepancy in the timecodes between cameras. This is following previous tests where they matched. Is this a known issue?

Settings and FW on both cameras exact the same?
Have you set the cameras to Sync on SDI in? and use the same offset in lines?