Bionic ships with /etc/samba/smb.conf in a state that allows SMBv2 connections. No extant Linux GUI software actually works with it though. As a result, Samba share and printer network discovery is broken with Nautilus, Dolphin, and printer management software. The only way to access samba resources is to know the URL and manually enter it (e.g. "smb://myshare"), which is user-hostile and impossible for most users. How are people supposed to know the URLs of samba resources that they can't discover in the first place?
This has been reported at https://www.dedoimedo.com/computers/ubuntu-beaver-samba-shares.html, and I can confirm both the issue and the resolution:
Add "client max protocol = NT1" to /etc/samba/smb.conf. Boom, problem solved: Samba share and printer discovery suddenly works.
I recommend pushing this as an update to Bionic. Samba usability is //critical// for professional and enterprise usage.