I still haven’t found the origin of that message. I suspect it’s an Ldapproxy connection. However, it seems harmless, just log noise. I have the same message on my server, and everything works correctly.
For the other issues, I can only say that I’ve also experienced a similar problem after a migration. Share access by hostname didn’t work, but using the IP did. However, in that case, the required hostname was not the DC name but the NS7 one (the name of the file server). What seemed to fix the issue was adding an alternative servicePrincipalName with:
samba-tool spn add ...