A couple bugs to report:
#1: Unlocks from playing the campaign for Free Play mode (Characters and Karts) do not stay unlocked after exiting the game and booting it back up.
#2: Selecting more than 1 player in Free Play, backing out, and playing campaign will make the campaign multiplayer (or at least have multiple screens), but will then glitch out in menus.
#3: In the forest, sometimes there is a possibility that a jump pad (in the section with multiple jump pads) will launch you and cause you to miss the next platform (this happens regardless of player input).
I'll post more as we keep discovering them!