[Postman]

Hi, I don't have experience with the Decklink card so cannot help there but maybe I can put us in the right direction.

First question, do you really need audio pulldown? Syncheck audio is meant to play at speed with no pulldown, 48000 not 47520, against 23.976 picture. This might be the cause of your drift?

Second, how are you "deriving" 23.976 tri level from 29.97 bi-level? Does that mean you have genlocked a tri-level generator to 29.97 black that you are using for SyncIOs?

The frame edges of 23.976 will always be changing against 29.97 frame edges, even when the signals are gen-locked. There shouldn't be a drift over a long period, but there WILL be moment-to-moment misalignment of one's frame edges against the other's (due to different frame rates), so I would expect lockups to vary each time you hit play, but staying within a frame's worth of error. Maybe that is the cause of your Syncheck trouble?