since at least the latest version, Duplicati has been failing to back up my external drive.
It says the ‘source’ has 0 bytes, which is obviously not true. It seems not to be able to recognize the drive contents at all:
I’ve actually figured it out, now that I wrote the issue out.
After all, it seems to be a permission issue. Duplicati is not properly requesting permission from macOS to access folders, and thus it cannot see contents by default. I think a patch for support of this is needed here.
A workaround is running Duplicati as sudo from command line:
I don’t have macOS, but for Catalina compatibility you probably want the current 2.0.5.1_beta_2020-01-18 because Catalina had a large number of security changes that Duplicati had to deal with, but not in a 2018 Duplicati which is basically what you have. 2.0.4.23 was just a warning added to 2.0.4.5_beta_2018-11-28.