The 'Rockstar Transformation' glitches on occasion, showing the fireworks show and play the music as intended - but the character model will play the 'Speedster Transformation' animation instead. An additional (occasional) glitch will render the character model completely invisible unless I start moving. Note: I do not possess the Speedster Transformation on any character.
I am not able to determine if there are other animations glitched, especially since I've had this happen inconsistently.
Anecdotal evidence suggests I'm not the only player with this glitch.
If there are others with transformation glitches, please add them below.
In-game, I'm The_Kef -- ¯\_(ツ)_/¯ "That's really it for Champs."