Mapping Error

I have a Sky Router and "Q Box" TV service. These are connected from the router, as my network:

* Sky Q Box, wireless.
* TP Link 5-Port Gigabit Desktop Switch, TL-SG105, via Cat 6 ethernet, 2 rooms from the router. This is then connected to this -
* Desktop I am using -
* nsa310 NAS, both via Cat6 ethernet.
* Wife's Lenovo laptop, 9 months old, 1 room away at the other side of the bungalow but very close to the router: wireless, permanent full signal.

Every device works fine, I can print from the laptop, printer is beneath the desktop and USB connected.
The problem has only just happened in the last couple of days: when opening "Network & Sharing" I cannot locate anything other than my desktop and internet. If I try to "See Full Map" I get the message "An error happened during the mapping process."
I have tried to solve this via Windows Diagnostics, have used Command Prompt as administrator to carry out these commands -
sfc /scannnow (no problems found)
ipconfig /flushdns
netsh int ip reset (ignored "Restart computer" -went to) : -
netsh winsock reset (Restarted computer there)
No change.
This has always worked for me with DNS problems and mapping errors in the past, but nothing I do seems to help. Strangely, when I use Windows Explorer to access the network, I can see all devices that are on the network and live. Currently, that's this PC, the laptop (granddaughter doing homework) and the NAS. I am stumped: does anyone have any ideas? I would like to carry out my usual backup to the NAS using Macrium Reflect, if there is a problem during backup, I do not want to experience a failed backup.
The only unusual activity has been an upgrade to Kaspersky Total Security 2017, from 2016. No problems with that.

I have no idea where the gremlins went, but after posting this, I reopened Network & Sharing - See Full Map. Great, I thought, it's solved all by itself. Tried it again, back to the problem. Going to have lunch and come back to this. Shutting down and switching off the desktop, back laters.

I hate these kind of on-off problems!

Back on today (Monday) : surprised no one has answered. Anyway -

Libraries - Windows Explorer - Network shows all devices. Network& Sharing Center gives "Windows cannot discover any computer or device." I accessed the Sky router page and even the 3 phones in the house were shown on the webpage. WTF is happening with Network & Sharing Center?