Further on the disk i/o error (normally seen as causing the lock up for me):
Looks to be only caused by very specific files (and only those files) such as Duplicati db in /AppData on certain systems as far as I can tell. One system doesn’t ever seem to have a problem backing it up but the other one often throws disk i/o on it and that’s one error thrown during the WhenAll() that causes the total lockup of the Duplicati UI.
I intend to look into why certain files do that as there’s probably something Duplicati should be looking at so as to not attempt to back it up, or in the worst case it should at least throw the disk i/o error, then remove that file from the backup and continue - since there’s a ton of stuff in the code here, it would take me a while to sort through what exactly needs to be done, and so I may not go that far with this.
For now, just blocking the files where this happens such as Duplicati’s AppData folder from the backup, appears to fix the situation until a better way to handle it is implemented. I have backups running without anything bad showing up for well over a week now and that wasn’t possible before.
Theory: At least with Duplicati’s db file, it could in theory be getting into a situation where its attempting to write and read the file at the same time. Perhaps with a slow enough system (eg the one where its happening for me), it runs into a problem and disk i/o error gets thrown. Could include or be another difference such as larger backups that I didn’t duplicate on other systems without the problem.