I currently have a backup job. When I check it using fdbbackup describe , most snapshots show restorable=false . Does this mean these snapshots cannot be restored? However, after I run fdbrestore , the previously restorable=false snapshots become restorable=true . Why does this happen?
Hello 
Have you try to run fdbbackup describe with the --deep option?
It might help to refresh the cache.
I just learned about this option now – thank you so much for explaining!