Not sure what happened. I completed two of the Strike Fragment quests and was awarded two Memory Fragments that went to my Postmaster despite having room in my inventory. Upon claiming them, they simply...disappeared? Not in Postmaster, but not in Inventory either. I claimed them manually (not through Vault-managing software or apps) so I'm not entirely sure what caused the problem. Considering the time it takes to complete the quests it's frustrating and should be looked into.