Issue on CANON R5C with CF Express showing less time remaining than SD Card.

[ldispi1]

Hello everyone, I have a very bizarre issue with my new Canon R5C.
I’m recording 4k50p or FHD50p mp4 Clog (I haven’t tried other resolution or formats) with double slot recording mode onto 2 brand new Sony Tough 128GB SD and CF Express formatted directly from the camera.
The camera initially shows a 7 minutes difference between the 2 cards (CFexpress has less time).
While shooting I noticed that the time gap increases exponentially (almost a 40 minutes difference) at the end of the shooting.
I also shoot 120p slow-mo on the SD Card so at the end of the day I have more space occupied on the SD Card (still showing more time remaining than the CF E.).
The CF E. has less space occupied but still less recording time remaining than the SD Card.
What could possibly be the source of this problem?
Let me know if you have experienced the same issue.
I have flashed the latest firmware: 1.0.8.1
P.S. After some more testing I tried recording until the CF E. said "END" and to my surprise it was only half full.
I really don't know what to do anymore.
Thanks in advance for any kind of help.
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CARDS USED:
-Sony SDXC Pro Tough 128GB Class 10 UHS-II U3 V90
-Sony Tough CFexpress type B 128 

[AtticusLake]

I tried this, but I can't reproduce it.  I don't have the same setup as you -- my smallest CFExpress card is 512 GB -- but I got as close as I could.

So I have a 512GB CF Express, and a 128GB SD.  I set the camera to "Double slot recording", MP4 YCC422 10-bit, 4096x2160, 225 Mbps, 50.00 FPS.

The run-times at the start were shown as 297min and 74 min; at the end were 235min and 12 min.  IOW both went down by 62 minutes.  The file sizes on both cards were the same, 99.1GB.

So, it's all behaving as I expect.

I can only suggest that you make sure both cards are recording the same format; the remaining time shown will depend on what exact format you're recording.

Other than that, it sounds like a bug in the CF Express card, which for a Sony Tough seems unlikely.  Could it be fake?  Face cards are often lower-capacity cards with the firmware hacked to show a higher capacity.