Sideswipe, Ratchet, Arcee, Wheeljack, and Ironhide get their cutie marks swapped on accident. Because of the swap, their personalities are different and they're incapable of their specialties. As a result, they do the jobs based off of their "wrong" cutie marks but they can't do that job either. Bumblebee has no choice but to watch them fail.

Their cutie marks were swapped due to a spell, but unintentional. Bumblebee didn't do the spell, it was probably from a young unicorn (probably from Bridlewood) who accidentally did the spell when they were trying to do something different.

Original version:
https://www.deviantart.com/small-brooke1998/art/MLTF-What-My-Cutie-Mark-Is-Telling-Me-848033237