Sites don’t load with the NextDNS iOS app, but do load with 3rd party app using NextDNS DoT config

When using the NextDNS App on iOS 14.1, no sites will load at all in Safari or third party browsers. I’ve tried it with and without custom configuration IDs, and it hasn’t worked. 
 

However, when I use a third party app like PrivateDNS and set the DoT url to [ID].dns.nextdns.io, everything works perfectly. 
 

I don’t if it’s an iOS bug with a specific protocol,  since the NextDNS App doesn’t specify whether it’s using DoT, DoH, or IPV6. All I know is if I change the DNS source to NextDNS app, I can’t load any websites.