While I was doing “The Getaway” quest in the Undermine, I joined a group for a raid. I was getting summoned, so I left the vehicle that is required for the quest. Whenever I left the vehicle, the Action Bar for the quest using the Boomballs stayed past the summon into the raid from the group. I could not use any of my spells in my spellbook, and I had no access to my normal action bars. I logged out and back in, exited the game, and even died to try and get it to reset, but none of it worked. My character is completely useless and unplayable at this moment because the Boomballs do not do damage outside of the quest. I saw someone on the EU forums talking about the same thing happening to them and they said that even unstuck didn’t help their character. Here is the link to said forum post: https://eu.forums.blizzard.com/en/wow/t/stuck-with-vehicle-ui-on-vehicle-exit/563521
The problem has been fixed. The person on the EU thread learned that you just had to get into a two-seated mount with someone else to fix it.