I’m using the Runebound Firelord mount and when I’m ascending from the ground using Skyward Ascent (or just double jumping) the game usually disconnects me.
My friend also reported the same issue while using Machine Defense Unit 1-11.
I can’t replicate it all the time, since I’m not sure what causes it. It seems this happens when the terrain around the mount is not clear or flat… maybe on a slope or if there are rocks or any debris around the player.