Wild speculation here: In an earlier post, (assuming this thread is about the same system), you had NVLink enabled.
Assuming you have removed the NVLink bridge, do you still have the --sli="mosaic" entry in your xorg.conf?
If so, I wondered if it could be contributing to the anomalous results.
I see your cards using NVLInk are capable of 112GB/s, (presumably 56GB/s each way). Out of curiosity, why are you no longer using it?