Try formatting exFAT on the PC then insert into phantom and redo test.
mSD card formatted exFAT in the P3, removed to computer, verified exFAT in the computer, copied on firmware update, placed in P3.
exFAT is exFAT, doesn't matter where it was formatted.
The 18 month old camera chip that is used for the P3 camera may be limited to 32 bit processing. Lots of weird camera firmware issues have been popping up, all of them revolving around the low level interfaces with the camera chip. I think it's more likely that DJI just used the basic firmware sample from the camera controller manufacturer. It's really too bad, there is a lot more capabilities in the chip that DJI is not taking advantage of.