I just built 19.07 for x86 and the upgrade went very well. I was using samba36 in 18.x and had some trouble browsing, so I decided to try to fix it and upgrade to samba4 to match my client.
Now I can't get samba4 working. The first problem seems to be that when /etc/init.d/samba4 dynamically builds smb.conf, it doesn't include the configured share...at all. It's just completely missing from smb.conf. Does anyone else see this?