Error "Object reference not set to an instance of an object" during mailbox backup with Veeam Backup for Microsoft Office 365

Veeam Backup for Microsoft Office 365
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Mailbox backup may fail with error:
"Processing mailbox failed with error: Object reference not set to an instance of an object."

You will also find these entries in "C:\ProgramData\Veeam\Backup365\Logs\Veeam.Archiver.Service_%date_time%.log" log:

Processing mailbox:
Syncing folder items: name...
Sync time: 0.562066
Changed items: 26, deleted items: 0
Estimated changed items size: 1.77 MB
Error: Object reference not set to an instance of an object.
   at Veeam.Archiver.Source.SyncPage.SaveChanges(IFolderRepository repository)
   at Veeam.Archiver.Source.ItemProcessor.ProcessFolder(Byte[] id, ExFolder folder, Byte[] currentState)
   at Veeam.Archiver.Source.ItemProcessor.<>c__DisplayClass6_0.<Process>b__0()
   at Veeam.Archiver.Source.FolderRetry.<>c__DisplayClass14_0`1.<Process>b__0()
   at Veeam.Archiver.Source.FolderRetry.Process(Action action)
   at Veeam.Archiver.Source.FolderRetry.Process[T](Func`1 func)
   at Veeam.Archiver.Source.ItemProcessor.Process(ExFolder folder)
   at Veeam.Archiver.Source.FolderProcessor.DoMailboxWork(CancellationToken cancel)
   at Veeam.Archiver.Source.MailboxAction.DoWork(CancellationToken cancel)
Mailbox processing failed:


If you running version or older, the issue has been resolved in Veeam Backup for Microsoft Office 365 1.0 Update 1.
If you running version or newer, contact Veeam support directly to obtain the fix.

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