Holding movent keys while being teleported can sometimes cause the avatar to stick in the flying animation until animations are reset via the avatar menu.

This bug has been around for a long time, though i would try reporting it again.

go to

get a "Teleport Ticket" from the sign and wear it so you can use the portals.

Walk into the portals while holding forward until the flying animation sticks.

It can be hard to reproduce when you want it to happen, but it happens to me all the time.