Researching it a bit more, I must admit that while I am better informed, I’m none the wiser…
At the start of the shoot day, the timecodes in the paper log and in the media files in Premiere match (at least, they’re very close, within the limits of human error during a preroll). (I don’t have access to the raw media files on the CFast media, so I can’t compare them to the ones in Premiere.)
As the day goes on, they drift apart. Interestingly, they drift apart by pretty much 29.97/23.976 (1.25), with the media “ticking” faster than the paper log.
I have absolutely no explanation for this! Next time we shoot with this workflow, I’ll do a test shot and ingestion to see if I can figure out what is going on.
The footage itself is fine, and seems to be clocking properly, so the error is in what’s in the paper logs.