I think someone should place a guard in Streamblocksplitter.cs for the hashcollector. It’s possibly empty and so there can’t be any blocksetentrys. A check before the final insert in LocalBackupDatabase:AddBlockset would also be nice. I bet in those cases there is no entry in the specific foreach-loop. The easiest explanation at first glance would be a closed stream in the while-loop …but this can’t explain a generated “filehash” for the blockset.