Thanks for the followup! I tried with the latest 4.8. That gave those credit errors under 10.13.6, but I just finished an initial backup under 10.14.1 in one go, so it seems Apple may have fixed something.Yes, I have. And mostly without issues. I did have some credits errors, and reported them to Apple. They replied and investigated quite extensively.
Some of them seemed to be caused by bugs in Samba. Have you tried with the newest versions?