Since installing a firmware upgrade in January, I've noticed that my hardwired connection to my router seems to go dead (no connection) while other ports remain working. I am using a Windows 10...

Mega thanks! That was it!

I rebooted the router and the flashing WPS light disappeared. I then (via the Edge browser) tried to set DoS with no success. At your suggestion, I've tried both IE and Chrome and got the same...

On my Securities -> Setting page, DoS protection is off and I can't turn it on. Also I just noted that, for some reason, the WPS connecting arrows on the front of the router have been blinking...