A better log than the one-line default (which unfortunately drops most important details) might help.
Live log at About --> Show log --> Live --> Warning is one, or for long-term you could set a –log-file.
Reporting options also seem pretty good at emailing some of the detailed messages when jobs fail.
A completely different approach would be to see how Windows running as your Duplicati user does. Sometimes files have permission issues, or are locked. (–snapshot-policy can help get locked files).
Fixed issues with long paths and USN, thanks @dgehri
Rewrote path handling across the project to better support long paths, thanks @verhoek
Issue 3311 PathTooLongException when using USNJournal #3456 looks like it went in Nov 8, 2018.
Although not relevant to current topic, latest beta came from v22.214.171.124-126.96.36.199_canary_2018-11-08 meaning possibly it could show some long path problems. For current topic, I’d suggest a log check.
Can’t find it here on 188.8.131.52_canary_2019-11-05 over all four combinations of VSS and USN on/off however I’m seeing a worrisome non-detect of added files with USN on and VSS off. It needs a look.