Shared Folders LAN Issue, on 1 PC, Since Yesterday's W10 Update

Hello,
Firstly, I am not an expert -or anywhere near it- when attempting to diagnose OS issues, so any responses with technical instructions will most likely go over my head.

Since I updated my HTPC with the latest W10 update -'Feature Update to Windows 10, 1703'- I have been unable to connect it to 2 computers on my LAN. The LAN architecture is as follows:

Modem router (TP Link ADSL)>ArcherC5 (AC1200 Dual Band Gigabit Router) -all other connections through C5:
>1) Desktop PC wired to C5 router -w10Pro
>2) Bedroom HTPC (Asus Beebox SFF box) wireless to C5 router on 5GHz -W10Home
>3) HTPC (one with issues) wired to C5 router -W10Home

Both 2 & 3 PCs can connect to each other, both via shared folders & Homegroup. But not to PC 1.
I can ping PC 1 from PC 2 & 3, but any connection is not visible within File Explorer. Also, can ping from any PC to any other. PCs 2 & 3 are on static LAN IP addresses. I tried using automatic IP address, but no-go. The internet connectivity has NEVER been an issue.

I tried releasing & renewing the ipconfig on the pc3. But am unable as 'The operation failed as no adaptor is in a state permissable for this operation'. What that means I have not checked, as I don't know if I am proceding down the proper diagnostics path.

I have tried other posted ideas, on this forum section -https://www.tenforums.com/network-sharing/34589-network-devices-not-showing-file-explorer.html- as well as other possibilities.

I tried resolving it using the 'incoming connections' troubleshooter & got the following: 'More than one device is performing Network address translation (NAT)', from PCs 1 & 3. Not sure about PC 2. Don't see how this could be cause, as I've never adjusted settings on desktop rig -PC 1.

Also tried creating a new Homegroup from PC 1, but the other 2 PCs could not recognise it

That is about the extent of my ability. Don't know what else to, apart from reinstalling the True Image backup from just prior to the update, which I am about ready to do, if nothing else presents itself in the near future.

Any & all dummied-down ideas, etc. would be greatly appreciated. Thanks for a great site.

Seeing as how this issue had presented itself, & I am off work recovering from surgery, I thought I would take the opportunity to give my PC area a major spring-clean. It was on my to-do list for some time.

I totally disconnected the entire system, relocating my TP-Link W8960N modem & Archer C5 router to higher positions, in an effort to gain whatever wireless signal, to my bedroom HTPC I could. After reconnecting all devices & cables, guess what, I now have bi-lateral connection between all 3 PCs. The only thing I did was logon to the wireless modem & disable that component of the device.

I don't know what could have resolved the issue, but it is resolved. If anyone could suggest a reason why it rectified itself I would love to know.