Since some weeks, perhaps since updating Duplicati to version 2.0.8.1, sometimes the warning comes up
2024-09-18 14:05:49 +02 - [Warning-Duplicati.Library.Main.Operation.Backup.MetadataGenerator.Metadata-MetadataProcessFailed]: Failed to process metadata for “M:\Path\to\file.sfx”, storing empty metadata
InvalidOperationException: Unerwarteter Methodenfehler 59.
(“Unerwarteter Methodenfehler” (german) → “unexpected method error”)
file.sfx is no system file, just a random file of a subfolder.
M: is a mounted network shared drive (local OS: Win10, remote OS: WinServer).
The warning appears at one or two files at the backup run, but only occasionally ~ on average every third run.
File is usually one that was not touched or altered since years. And not since last differential backup run.
File type seems to be unimportant - .txt, .jpg, .html ; also file size differs from 1k to several MB.
If I had to do a wild guess, I would blame the slow server with its slow virus scanner; perhaps the virus scanner blocked access too long, so Duplicati didn’t wait long enough and marked the data as “not accessible”. But - only a wild guess.