When a Gum Worm is nearby, crouching to descend in an Immersive Aircraft vehicle causes the player to exit the vehicle unexpectedly, leaving it stuck mid-air. I'm not sure if there are other similar issues like this.
Reloading the world is required to get it back to normal. (However, if you re-enter the vehicle, the same issue will occur again.)
The following footage shows only the mods listed below installed, with no additional mods, and all are the latest versions:

ModLoader: NeoForge 47.1.106
alexscaves-2.0.2
citadel-2.6.0-1.20.1
immersive_aircraft-1.1.2+1.20.1-forge