If you do a dungeon or fate that is lower than your current level, you're forced to be level synced.
Reason why is cause some skills require a certain level in order to be used.

So say you're heading into a level 10 fate, and you have Huton up and Wasp. Those two are automatically removed because it'd be unfair for others to have an advantage.

Same goes to dungeons like Dzamael Darkhold and Aurum Vale.

Not a bug, it's working as intended.
Yeah yeah, it's annoying, but really.