I'm not sure where to get support to trouble shoot so as nothing has changed and everything has stopped working I'm assuming there's some issues going on at NextDNS.
At ping.nextdns.io I get the following:
vultr-lon 20 ms
■ anexia-lon 20 ms (secondary)
zepto-lon 21 ms
zepto-bru 24 ms
netbarista-par 25 ms
anexia-par 27 ms
vultr-ams 28 ms
zepto-ams 28 ms
virtua-par 31 ms
estnoc-bru 32 ms
■ dns1.nextdns.io error (primary)
and domains like "https://my.nextdns.io" failed to get resolved and wouldn't load. I went onto my 'backup' DNS of 220.127.116.11 and everything worked perfectly. My router does DoT and my network submits requests direct to the router. Everything was working perfectly and now nextdns doesn't resolve.
Switched everything off and switched it all back on, but it looks like nextdns is down. Can someone try switching NextDNS off and back on again please.