Peer networking issue - invisible PC

There are 6 PCs on the network, a mix of W10 pro, W10 home, and W7 pro, and a mix of WiFi and cabled

One PC is set up as a "server" (file, print, RDP) and all the rest are user PCs

All but one of the clients is able to access the server, connecting to a shared printer and Remote Desktop on the default port 3389

Here's the problem pair: -

Server:
- Windows Defender firewall ON (with obvs the automatic holes opened when you set up file & print sharing & allow RDP)
- Windows 10 Pro 1809 (17763.503)
- SMB 1.0 / CIFS file sharing support ON (all 3 sub-options)
- Network discovery & automatic setup of connected devices ON
Client:
- Bitdefender firewall ON (but it makes no difference if I switch off ALL Bitdefender protection)
- Windows same version: 10 Pro 1809 (17763.503)
- Same SMB settings: SMB 1.0 / CIFS file sharing support ON (all 3 sub-options)
- Same Network discovery & automatic setup of connected devices ON
...in fact I can find *NO* differences in any settings, except as noted above for firewall - nothing that should make any difference, and nothing that shouldn't.

Both obtain IP by DHCP from the SOHO router, with the server's fixed (reserved) while all clients are random. There is nothing in the router's DHCP to differentiate between configs of static and dynamic allocations.

Yet 4 of the clients are able to access Remote Desktop and print to the server; the 5th one just won't connect: -
(a) RDP connection attempt: Connecting to: {servername} - Initiating remote connection... ...times out with "Remote Desktop can't connect to the remote computer for one of these reasons..." {etc etc}
(b) Attempting to add remote printer: (Select a shared printer by name) - I type in \\{servername}\{printername} and [Next]...Connecting to {printername} on {servername}...
... times out with "Windows couldn't connect to the printer. Check the name {etc etc etc}"
(c) Attempting to connect to server file share: (browsing the network sees other PCs, and itself, but not the server). Enter \\{servername}\ in address bar
...times out with "Windows cannot access \\{servername}\ - check the spelling {etc etc etc}"
(d) Attempting ping from server to client by NETBIOS name: Pinging {pcname}.local [IPV6 address]: destination host unreachable
(e) Attempting to ping from server to client by IP 4 address: destination host unreachable
(f) Attempting to ping from client to server by name: Pinging {servername}.local [IPv6 address]: Request timed out
(g) Attempting to ping from client to server by IPv4 address: request timed out
(h) (at night, only three live devices on the network): Using "fing" network discovery tool from server: detects only itself and the router
(i) (at night, only three live devices on the network): Using "fing" network discovery tool from client: detects itself, the router, and the server (by name).

It looks like something on the client is blocking any traffic from the server, but what? I may have tried some other stuff I have forgotten to mention - I've been at this for two days now with no change in results. But I've run out of ideas and would welcome any input.

Thanks
Chris

Addendum: I set up Remote Desktop to connect from client to server via its URL ({servername}.hopto.org, set up via no-ip.com) and it works just fine even though both machines are on the same LAN. Whether the traffic actually goes out on the Internet and is routed back in, or is just translated by the router I don't know but I doubt it's that important...?

- - - Updated - - -

Caledon Ken said:

Have you done a Network reset on the troubled device?Ken

Good point. No I haven't; that sounds like a logical next step. Unfortunately I'll have to be on site to do that though, as opposed to comfortably doing it via TeamViewer which I have to admit is becoming my lazy man's support method of choice

Thanks Ken, I'll give that a try tomorrow

Can you connect via IP run thi scan on a few pcs can they see the pc and can it see other and which pc is the master browser NetBScanner - NetBIOS scanner

Caledon Ken said:

Have you done a Network reset on the troubled device?
Start > Settings > Network and internet > scroll down right hand side > Network Reset. This may require you to reconfigure any special comm software like VPN's.

So I ran a utility from Major Geeks called "Complete Internet Repair Tool" which has a whole string of networking components that you can reset and I let it do most of them (leaving out irrelevant stuff like IE11) and - no difference.

Caledon Ken said:

After that I would run these six bolded commands. Use a Command Prompt(admin) or Powershell(admin)
Ken

AFAIK the CIRT does all these but I did them manually anyway - still no difference

I also uninstalled Bitdefender - nope

I also ran NirSoft's browse master scanner and it showed me no more information than I already had - the troubled PC could not "see" the server but all the others could, and the server could see all the others.

Eventually in desperation I changed the fixed IP address of the server in the router's DHCP reservation and Bingo. Just like that, everything started to work. I didn't even have to force the server to release/renew its DHCP lease; when I checked ipconfig it had already picked up the new address.

Guess I should have expected something like this. Not the first time I've seen slightly "anomalous" networking behaviour from a SOHO router. Should I mention the brand name? Probably not (it's a Netgear).

Thanks for the input. Keep up the good work :)