Is that lines under an “Error-Duplicati.Library.Main.Operation.TestHandler-RemoteFileProcessingFailed]: Failed to process file”? If so thanks. If not, are you sure it matches the original issue? New log might be:
The Operation is not valid for the object’s storage class
and if you want better information, and know S3 facilities and config (I do not), you can do a web search. What I found when searching that error message was usually people talking about Glacier, as above did.