A teensy tiny bit of difference in the alignment of the pots is not out of the ordinary. In practice, you really ought to be just putting the trim-gain pots wherever necessary to get a nice level on each individual track as they come and not be concerned about a particular spot you’re keeping them at.
The pot stems might not be exactly aligned internally to the degree-seconds.
The music might not be exactly at the same time when looking at the metering. Were they all exactly in-phase? You might want to try a test tone with the speakers/headphones off to confirm whether the pot stems are way off or not.
These pots are quite touchy the lower you go on them, sort of similar to the MP2015, though the Rane’s a lot more touchy and has some gain structure and input pad problems.
You also appear to be running your input trim-gains rather low. Just stay out of the blue (on purpose, anyway), and leave the top white for that old funky disco track that needs some extra oomph.