One player in split-screen mutliplayer can walk through leaves; other players can't.
Looking at search many similar issues are marked as dupes of MCPE-109925 but noone here had elytra.
Related issues
Comments
[Mod] OcelotOnesie
Nixinova
We are tracking all cases of the player not switching out of the elytra gliding hitbox at MCPE-109925.