This has started to happen since the fix for bug 1043115 was added to Samba 4.6.7. The net rap server domain -S master-browser command now fails by returning an empty list of servers despite there being 4 servers in my lan all with valid shares. This causes SMB4K to fail and remove the workgroup name from the SMB4K window rather than displaying the servers in the workgroup had the net command worked.
I have created bug #1057148 in bugzilla for this issue.
Stuart