Every player hits the final lap at a different time. As a result, music-based events may occur at different times on different players' systems. Normally this isn't an issue because they're mostly cosmetic, but one notable instance where they're not is Music Park - the Bouncing Notes allow racers to do tricks when they hit the ground every 8 beats.
In theory, this means that everyone else will be bouncing upwards and doing tricks when it doesn't look like they should, but I haven't really noticed this happening. How does online play deal with this discrepancy?
(I'm pretty sure this wasn't an issue in MK7 because the notes' bouncing stopped matching the music after 1:52 had passed.)