final update - this fix offered by @Matt worked perfectly for me. You might also need to restart the cloudberry-backup service

This is a slightly aging post, but I just wanted to add a note - this did help quite a bit, but I'm still getting more issues than I like. More research to come. My system runs Mint 19.3 (Ubuntu under the hood).

Here's the link to the mac/linux knowledge base with similar advice: link, but Matt's suggestion to specify root is not present in the KB.

Thanks, @Matt for the tip!