I was working on a map in a function, that detected when you were jumping in air by using elytra's. So it tested if you were flying, removed the elytra and added it back a tick later. But i also had a reset system that sent you back to the lobby when you were on the ground. But because of this bug, when you removed the elytra in the air, it thought you were on the ground. I think it is related to this bug:
https://bugs.mojang.com/browse/MC-112344