This issue is still present in Buster. Changing the interface name to its IP address in smb.conf does not make sense because we're talking about a situation when your IP address is managed by DHCP.
Tweaking the systemd service files does not help according to the OP, and even if it did, this is not a solution - network-online.target apparently still does not work. Mathieu, is there a bug report with more details about the network-online.target problem? It looks pretty serious since it can potentially break all network-based daemons, and is still not fixed in Buster. -- darkpenguin