I had my Netgear router setup to use 18.104.22.168 for DNS and up until a couple of days ago it was fine. The issue manifested as DNS errors on my PS4 when trying to download game updates and the PS4 Youtube app being unable to sign in. Also the odd message on my iPad about WiFi being disconnected, when it wasn't.
Changing the PS4's DNS setting to the Google ones as a test fixed the PS4 issues so I have changed my Netgear back to using the VM DNS servers and so far all seems well.
This thread on the Cloudflare community suggests I am not alone: