Hi,
I doubt that this is the only reason, but certainly a contributing factor. The ADC used in the 15M is a 8bit, which resolves the 5V to steps of 19,53mV. The delta between 157 and 170mV is 13mV, this equals roughly one ADC step. So the fuel values would slip one row, which is noticeable but not to the extent of what you describe.
A re-sync is what I would do.
Cheers
Meinolf