Also, I think the staff might be able to fix the unloaded chunks problem by copying and pasting the world back to exactly where it is now (on PC), then saving it. This should update all the chunks, then save the world.
Well, likely because the sitting state is just slightly different standing. When moving to sitting/sleep, your character visually snaps to the correct position, but if you get up on the spot (i.e. by attacking in a direction that would make you stand from sitting on a chair/toilet or sleeping, or by interacting with the specific resting state furniture again), you see that your only movement is visual; you’re still in the same place, same coordinates when going from sittiing/sleeping to standing and vice versa without moving. As a result, when you move to the sitting state on the clientside floating bench, the game tries to make you “stand” in that location which you’re held at while in the sitting animation. But because there’s no ground for you clientside, you end up falling, and because there’s no player state of standing still and falling at the same time, falling takes priority because it’s movement. And because of the movement, the resting state is cancelled, hence why you can’t sit there, nor will you appear to be sitting while falling.