Unable to backup

Did you try to change or remove the passphrase? The goal was to see the original failure, not this.
You might also be able to do a GUI run with About → Show log → Live → Information, or Verbose.

As a guess, though --auto-cleanup=true can sometimes cause this sort of thing. Try a remove?

EDIT:

Thought fixed in Canary Oct 11, 2021 by

Create custom Exception for remote list verification failures #4520)

2.0.6.100_canary_2021-08-11

Reduced number of cases where database cleanup is triggered, thanks @warwickmm

but if you’re on 2.0.6.3_beta_2021-06-17 you don’t have that fix yet.