Do you know what version of DSM you are running?
The most recent: DSM 6.1.4-15217 Update 1
I’m going to update the topic title to indicate it’s Synology issue in the hopes that somebody who has access to one can replicate the failure.
So, realistically, chances are very low.
Why not just run a debug version of Duplicati to track errors and find a solution? I could also give you remote access for experiments.