I seem to have the same issue that so many of others have had trying to set up Sabnzbd in docker via the UI. I've been using Sabnzbd for years but I am new to docker and a novice at linux. I've read through a ton of forum posts but I am still missing something. The problems start when I try to move the config folder and downloads folder to shared folders (it works fine if I let it stay inside of the default container).
The first sign of trouble is that in the container config it writes in new config statements after I saved mine.
Once I get it fired up I can see that the default base folder is "/config" and that while it will let me navigate to my "Downloads" folder it errors out on save with "Cannot create download_dir folder /sharedfolders/Downloads/Temporary".
I know that I am missing something fundamental - I've spent hours reading through various forums. One other note - I noticed in the SABNzbd log that the UID and GID are "911" - not sure where this value is coming from or if it matters. I am running it as root but I did try to add that value in here instead of "0" but that didn't work either. Any assistance would be greatly appreciated and I hope that I can pay it forward someday.