Just to add my tuppence worth to this.
I run Ubuntu on my desktop and with rc3 I am unable to see any of my Unraid machines on the LAN in my file browser, tried a few different file managers on my laptop, didn't make any difference at all, tried altering my SMB settings in Unraid, again didn't make a difference at all, downgraded to 6.7.2 and my machines reappear on the network browser in my file manager.
However even on rc3 I was able to browse my network shares by addressing them directly in the file manager with smb://192.168.0.100/$share or smb://matrix/$share
So I think that this all points to an issue with smb.
I have one machine with netbios enabled and one without netbios enabled to test. Both are discoverable on v6.7.2 neither are discoverable on rc1/rc3.
My main machine is the local master via the Dynamix Local Master plugin.
EDIT: Actually when I've written rc1, I should have written v6.7.2, dunno what I was thinking. Have edited my post to reflect this.