Hey Kev,
Yep, this is a known issue and has happened to a lot of people. It's currently bugged as it won't be sent to the Postmaster if you don't have space in your inventory.
Bungie are aware of this bug and are currently investigating. Here's a thread with more info from Bungie: https://www.bungie.net/en/Forum/Post/123284529/0/0
English
-
Thank you all... So i need to re-loot it?.. Great...
-
Yeah, pretty much. Sorry!