Repeatedly hitting Null Reference Exception

Running 2.0.5.1_beta_2020-01-18, on a backup set to Wasabi, I’m getting the following. Help?

System.AggregateException: One or more errors occurred. ---> System.AggregateException: Object reference not set to an instance of an object. ---> System.NullReferenceException: Object reference not set to an instance of an object.
   at Duplicati.Library.Main.Volumes.BlockVolumeWriter.AddBlock(String hash, Byte[] data, Int32 offset, Int32 size, CompressionHint hint)
   at Duplicati.Library.Main.Operation.Backup.SpillCollectorProcess.<>c__DisplayClass0_0.<<Run>b__0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at CoCoL.AutomationExtensions.<RunTask>d__10`1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Duplicati.Library.Main.Operation.BackupHandler.<RunMainOperation>d__13.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Duplicati.Library.Main.Operation.BackupHandler.<RunAsync>d__20.MoveNext()
   --- End of inner exception stack trace ---
   at Duplicati.Library.Main.Operation.BackupHandler.<RunAsync>d__20.MoveNext()
   --- End of inner exception stack trace ---
   at CoCoL.ChannelExtensions.WaitForTaskOrThrow(Task task)
   at Duplicati.Library.Main.Controller.<>c__DisplayClass14_0.<Backup>b__0(BackupResults result)
   at Duplicati.Library.Main.Controller.RunAction[T](T result, String[]& paths, IFilter& filter, Action`1 method)
   at Duplicati.Library.Main.Controller.Backup(String[] inputsources, IFilter filter)
   at Duplicati.Server.Runner.Run(IRunnerData data, Boolean fromQueue)
---> (Inner Exception #0) System.AggregateException: Object reference not set to an instance of an object. ---> System.NullReferenceException: Object reference not set to an instance of an object.
   at Duplicati.Library.Main.Volumes.BlockVolumeWriter.AddBlock(String hash, Byte[] data, Int32 offset, Int32 size, CompressionHint hint)
   at Duplicati.Library.Main.Operation.Backup.SpillCollectorProcess.<>c__DisplayClass0_0.<<Run>b__0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at CoCoL.AutomationExtensions.<RunTask>d__10`1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Duplicati.Library.Main.Operation.BackupHandler.<RunMainOperation>d__13.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Duplicati.Library.Main.Operation.BackupHandler.<RunAsync>d__20.MoveNext()
   --- End of inner exception stack trace ---
   at Duplicati.Library.Main.Operation.BackupHandler.<RunAsync>d__20.MoveNext()
---> (Inner Exception #0) System.NullReferenceException: Object reference not set to an instance of an object.
   at Duplicati.Library.Main.Volumes.BlockVolumeWriter.AddBlock(String hash, Byte[] data, Int32 offset, Int32 size, CompressionHint hint)
   at Duplicati.Library.Main.Operation.Backup.SpillCollectorProcess.<>c__DisplayClass0_0.<<Run>b__0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at CoCoL.AutomationExtensions.<RunTask>d__10`1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Duplicati.Library.Main.Operation.BackupHandler.<RunMainOperation>d__13.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Duplicati.Library.Main.Operation.BackupHandler.<RunAsync>d__20.MoveNext()<---

---> (Inner Exception #1) System.AggregateException: One or more errors occurred. ---> System.Net.WebException: The remote server returned an error: (400) Bad Request.
   at System.Net.HttpWebRequest.BeginGetResponse(AsyncCallback callback, Object state)
   at System.Threading.Tasks.TaskFactory`1.FromAsyncImpl(Func`3 beginMethod, Func`2 endFunction, Action`1 endAction, Object state, TaskCreationOptions creationOptions)
   at System.Net.WebRequest.<GetResponseAsync>b__78_1()
   at System.Threading.Tasks.Task`1.InnerInvoke()
   at System.Threading.Tasks.Task.Execute()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Amazon.Runtime.Internal.HttpRequest.<GetResponseAsync>d__16.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at Duplicati.Library.Main.Operation.Backup.BackendUploader.<<Run>b__13_0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at Duplicati.Library.Main.Operation.Backup.BackendUploader.<<Run>b__13_0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at CoCoL.AutomationExtensions.<RunTask>d__10`1.MoveNext()
   --- End of inner exception stack trace ---
---> (Inner Exception #0) System.Net.WebException: The remote server returned an error: (400) Bad Request.
   at System.Net.HttpWebRequest.BeginGetResponse(AsyncCallback callback, Object state)
   at System.Threading.Tasks.TaskFactory`1.FromAsyncImpl(Func`3 beginMethod, Func`2 endFunction, Action`1 endAction, Object state, TaskCreationOptions creationOptions)
   at System.Net.WebRequest.<GetResponseAsync>b__78_1()
   at System.Threading.Tasks.Task`1.InnerInvoke()
   at System.Threading.Tasks.Task.Execute()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Amazon.Runtime.Internal.HttpRequest.<GetResponseAsync>d__16.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at Duplicati.Library.Main.Operation.Backup.BackendUploader.<<Run>b__13_0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at Duplicati.Library.Main.Operation.Backup.BackendUploader.<<Run>b__13_0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at CoCoL.AutomationExtensions.<RunTask>d__10`1.MoveNext()<---
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