PCs keep randomly disconnecting from Internet.
When one PC disconnects, the others remain connected.
I investigated when a PC's Internet stopped working.
NIC's LAN status showed all was well.
I tried IPCONFIG /ALL, it appeared OK with IP Address, Default Gateway etc.
I tried logging into router but could not reach it, so it's clearly not the Internet but the connection between PC and router.
I disabled and re-enabled the NIC.
Now I was able to log into router, and Internet resumed working OK.