Opened a chest, nothing inside, relogged - Chest and key gone but no loot

You may have received a permanent Icon instead of a shard for something (plus some Essence). You wouldn't see any new loot if that happened. If you go into the Store > Account > Purchase History you can see if you unlocked any permanent content recently.

Other than that, I'd recommend posting on the Help & Support board. They can take a look at if you did receive something and give assistance from there.