Comment 9 for bug 1764853

Please attach these logs from when the login failure happens:
- /var/log/auth.log
- /var/log/syslog
- /var/log/samba/log*

I configured a VM with your smb.conf, joined a windows 2016 AD server via net ads join -k and AD users can login just fine immediately after a reboot.

I also used your netplan file, and I have no /etc/network/interfaces or interfaces.d/* content. I didn't upgrade from xenial, though, this was a fresh bionic install.

Since this is a VM I provisioned with uvt-kvm, there are a few differences from a normal desktop install:
- I did "apt install ubuntu-desktop" after provisioning the vm
- I removed the cloud-init package after provisioning
- my dns and dhcp server is not the AD server, although I used its DNS server temporarily when doing "net ads join" so that the server could be found

I could try a fresh bionic *desktop* install, I know it could configure networking a bit differently, or even install a xenial desktop and then upgrade, but let's start with the logs I requested above.