NextDNS suddenly stopped working

Hi, 

I've been using NextDNS Pro for around four years and my account is in good order.

The service just seems to have stopped working for no apparent reason and I can't figure out why. There have been no changes at my end (Unifi UDM). if I try to dig or use nslookup to query the DNS servers linked to my account, I get a timeout. I'm generally unable to access nextdns.io domains and had to use a VPN to log this. Swapping DNS on my router to Cloudflare, Google or quad9 works just fine.

I'm completely out of ideas for troubleshooting this one, so if anyone has any suggestions - please share!  

(UK/Vodafone)

Thanks in advance

FB