Found this answer which explains the values. So in my screenshot, the 'S-1-5-88-1-726139393' value is the UID of the share owner 'Administrator', 'S-1-5-88-2-726139380' is the GID of the share group 'Domain Users', and the 'S-1-5-88-3-16895' is a representation of the share's permissions in decimal form, in this case 0777.
It's not really denying permission, as the access variable is None, but annoying nonetheless.
Also, I do not have an issue joining the domain on 6.3.1. Left and rejoined as a test last night and that worked out fine.