HyperDeck Studio Pro 2 / ATEM PS4K Audio Sync Problem

Hi everybody,
after looking for a solution in the forums and finding only older posts, here's our problem:
A HDSP2 records 4Kp25 from an ATEM PS4K with audio coming from analog XLR inputs.
We did that before once for a longer take without problem, but on the last recording audio seems to have small dropouts that add to a slowly and irregularly rising sync drift - some dozen seconds over a duration of 2 hours or so.
SSDs are 850Pros, 1TB.
CODEC is ProRes LT.
Firmware of BM hardware is latest.
Cam is Micro Studio Camera 4K (embedded audio muted) going in ATEM, output of that to HDSP2.
Anybody already had a solution for this? (ATEM/HDSP2 thermal problems maybe?)
Best, Frank

EDIT: It's the video that seems to have drop-outs - audio is lagging behind.

Sounds like the exact same issue we had over the weekend, real nightmare.

Seems to just randomly happen for us. Full day of recording over the weekend and every file gradually looses sync. This has happened before but not for 9 months, nothing had changed in set up in-between,

Unless this gets properly resolved I guess the only way is to run a recoding and then check back, if it's loosing sync turn it off and on, repeat.