I can reproduce the issue on 18.04 with smbtree as well:
$ smbtree -U dummy
WORKGROUP
\\STORM
\\STORM\Users
\\STORM\print$ Printer Drivers
\\STORM\MySharedFolder
\\STORM\IPC$ Remote IPC
\\STORM\C$ Default share
\\STORM\ADMIN$ Remote Admin
\\AIRTOP airtop server (Samba, Ubuntu)
\\AIRTOP\HP-ENVY-5540-series HP ENVY 5540 series
\\AIRTOP\IPC$ IPC Service (airtop server (Samba, Ubuntu))
\\AIRTOP\print$ Printer Drivers
$ smbtree
WORKGROUP
\\STORM
\\AIRTOP airtop server (Samba, Ubuntu)
\\AIRTOP\HP-ENVY-5540-series HP ENVY 5540 series
\\AIRTOP\IPC$ IPC Service (airtop server (Samba, Ubuntu))
\\AIRTOP\print$ Printer Drivers
$ smbtree -U dummy
WORKGROUP
\\STORM
\\STORM\Users
\\STORM\print$ Printer Drivers
\\STORM\MySharedFolder
\\STORM\IPC$ Remote IPC
\\STORM\C$ Default share
\\STORM\ADMIN$ Remote Admin
\\AIRTOP airtop server (Samba, Ubuntu)
\\AIRTOP\HP-ENVY-5540-series HP ENVY 5540 series
\\AIRTOP\IPC$ IPC Service (airtop server (Samba, Ubuntu))
\\AIRTOP\print$ Printer Drivers
In the example above, STORM is the Windows 10 box, AIRTOP is another Linux box. Note how STORM is visible with or without username, but its shares only appear when a username is given.
I can reproduce the issue on 18.04 with smbtree as well:
$ smbtree -U dummy MySharedFolder HP-ENVY- 5540-series HP ENVY 5540 series
WORKGROUP
\\STORM
\\STORM\Users
\\STORM\print$ Printer Drivers
\\STORM\
\\STORM\IPC$ Remote IPC
\\STORM\C$ Default share
\\STORM\ADMIN$ Remote Admin
\\AIRTOP airtop server (Samba, Ubuntu)
\\AIRTOP\
\\AIRTOP\IPC$ IPC Service (airtop server (Samba, Ubuntu))
\\AIRTOP\print$ Printer Drivers
$ smbtree HP-ENVY- 5540-series HP ENVY 5540 series
WORKGROUP
\\STORM
\\AIRTOP airtop server (Samba, Ubuntu)
\\AIRTOP\
\\AIRTOP\IPC$ IPC Service (airtop server (Samba, Ubuntu))
\\AIRTOP\print$ Printer Drivers
$ smbtree -U dummy MySharedFolder HP-ENVY- 5540-series HP ENVY 5540 series
WORKGROUP
\\STORM
\\STORM\Users
\\STORM\print$ Printer Drivers
\\STORM\
\\STORM\IPC$ Remote IPC
\\STORM\C$ Default share
\\STORM\ADMIN$ Remote Admin
\\AIRTOP airtop server (Samba, Ubuntu)
\\AIRTOP\
\\AIRTOP\IPC$ IPC Service (airtop server (Samba, Ubuntu))
\\AIRTOP\print$ Printer Drivers
In the example above, STORM is the Windows 10 box, AIRTOP is another Linux box. Note how STORM is visible with or without username, but its shares only appear when a username is given.