OK Folks - (after sending a network trace to Microsoft), I have just had a reply back from Adam Rudell, Sr. Support Engineer, Windows Networking, Windows Beta.
"In reviewing the network trace, it appears that the HP MFP devices using NT LM 0.12(SMB1) only and does not support any other SMB version. I see the SMB:C Negotiate request coming from the HP MFP device, however the Windows 10 machine never responds back with the SMB:R Negotiate that should be expected. After about 15-20 seconds, the HP MFP closes the TCP connection to the Windows 10 machine. This may be due to a known issue identified with SMB1 over NetBIOS that will be fixed in a later build of tech preview, however I am not sure when. The reason your other devices are able to connect to the shares is that they are using SMB2 or SMB3 as the protocol medium to connect the devices instead of using the legacy SMB1 over NetBIOS (TCP Port 139) that was shipped with Windows XP / Server 2003. I would recommend to run the below script to ensure SMB1 is at least enabled, however you may have to wait until the fix is released in order to allow the HP MFP device to communicate with your Windows 10 machine. The other option would be to reach out to HP to see if they have updated software that allows the HP MFP device to utilize SMB2 or SMB3 (TCP port 445) to communicate with network share locations.
$smb = get-smbserverconfiguration
$smb.enablesmb1protocol
If the script returns True, then SMB1 is enabled" - (The script did indeed return True)
It seems to boil down to HP apparently still using SMB1, which currently has a "known issue" in Windows 10, rather than the newer SMB2 or SMB3
In a separate email, Adam also stated "SMB1 has been deprecated and will be soon removed from (MS) products"
I'm sure out of the currently 1 million or so Windows 10 installations, there must be a fair number who also have Networked Scaners / MFPs - so please HP can we have SMB2/3 support ?
ps. if anyone wants me to post the annotated trace snippets, please let me know (don't want to get told off by a Moderator)