Reply to bpms always off by .01 or .02 when mixing some tracks in serato itch with ns6?

hey i just got the numark ns6 a few weeks ago, and i noticed that sometimes when i try to mix songs they will match up fine, but some times the bpms will be off by .01 or .02, no matter how carefully i adjust the pitch, they dont match up :/ any idea why or if theres anything i can do about that or is it just how the song is? im pretty sure i have it set to the highest sensitivity (its on range 6)