Backup(s) failed with "Failed: Value cannot be null" error message than local storage requires repair

It happened 2 times on different servers.

Duplication Version: 2.0.5.1
OS: Ubuntu 18.04 LTS
Mono Version: 6.8.0.105
Backend: B2

After getting this error and try to backup manually we get Failed: Found 1 remote files that are not recorded in local storage, please run repair error message. After repairing local storage backups running normally.

I’ve also noticed that it already uploads some of the backup files (i can’t be sure if they are complete or not).

Failed: Value cannot be null.
Parameter name: path
Details: System.ArgumentNullException: Value cannot be null.
Parameter name: path
 at Duplicati.Library.Main.BackendManager.WaitForEmpty (Duplicati.Library.Main.Database.LocalDatabase db, System.Data.IDbTransaction transation) [0x00067] in <8f1de655bd1240739a78684d845cecc8>:0 
 at Duplicati.Library.Main.Operation.CompactHandler.DoDelete (Duplicati.Library.Main.Database.LocalDeleteDatabase db, Duplicati.Library.Main.BackendManager backend, System.Collections.Generic.IEnumerable`1[T] deleteableVolumes, System.Data.IDbTransaction& transaction) [0x00040] in <8f1de655bd1240739a78684d845cecc8>:0 
 at Duplicati.Library.Main.Operation.CompactHandler.DoCompact (Duplicati.Library.Main.Database.LocalDeleteDatabase db, System.Boolean hasVerifiedBackend, System.Data.IDbTransaction& transaction, Duplicati.Library.Main.BackendManager sharedBackend) [0x004a2] in <8f1de655bd1240739a78684d845cecc8>:0 
 at Duplicati.Library.Main.Operation.DeleteHandler.DoRun (Duplicati.Library.Main.Database.LocalDeleteDatabase db, System.Data.IDbTransaction& transaction, System.Boolean hasVerifiedBacked, System.Boolean forceCompact, Duplicati.Library.Main.BackendManager sharedManager) [0x00397] in <8f1de655bd1240739a78684d845cecc8>:0 
 at Duplicati.Library.Main.Operation.BackupHandler.CompactIfRequired (Duplicati.Library.Main.BackendManager backend, System.Int64 lastVolumeSize) [0x000a5] in <8f1de655bd1240739a78684d845cecc8>:0 
 at Duplicati.Library.Main.Operation.BackupHandler.RunAsync (System.String[] sources, Duplicati.Library.Utility.IFilter filter, System.Threading.CancellationToken token) [0x01033] in <8f1de655bd1240739a78684d845cecc8>:0 
 at CoCoL.ChannelExtensions.WaitForTaskOrThrow (System.Threading.Tasks.Task task) [0x00050] in <9a758ff4db6c48d6b3d4d0e5c2adf6d1>:0 
 at Duplicati.Library.Main.Operation.BackupHandler.Run (System.String[] sources, Duplicati.Library.Utility.IFilter filter, System.Threading.CancellationToken token) [0x00009] in <8f1de655bd1240739a78684d845cecc8>:0 
 at Duplicati.Library.Main.Controller+<>c__DisplayClass14_0.<Backup>b__0 (Duplicati.Library.Main.BackupResults result) [0x0004b] in <8f1de655bd1240739a78684d845cecc8>:0 
 at Duplicati.Library.Main.Controller.RunAction[T] (T result, System.String[]& paths, Duplicati.Library.Utility.IFilter& filter, System.Action`1[T] method) [0x0011c] in <8f1de655bd1240739a78684d845cecc8>:0

Yep, I am seeing a few other reports of this issue after compaction. You aren’t alone.