While fighting the dragon when it comes down to the center... to the portal.. and is vulnerable to melee attacks when it killed me and all my stuff dropped i could not see any of my stuff... it was there but invisible.. even the stuff that fell outside the bedrock portal shape... but upon walking around i could collect everything..

Now regarding Elytra... once i ender pearled through the small gateways to the end islands i could not use my elytra wings in creative or survival... and on coming back to the central island i still could not use them.. but on going back to the overworld they started working again..

i hope i was of some help... Cheers Devs !! ^-