Error Code: 224003

Can you make sure it only happens because of NextDNS first, you should just disable NextDNS and try again to remove the chances of other factors.

If it is caused by NextDNS could be that a domain is being blocked, so you should clear your DNS cache for your device, if you don't want to get too indepth just reboot the device that should do the same. Then enabling live logging and going on the App/Website that is giving you problems and see what's being blocked. You can either send the URL/Service name to me, blocked domains etc. Or just try yourself with manually whitelisting them, Doing a Google search to see what the domain is, if it says something about ads or tracking yeah it's probably bad and whitelist the ones that seem fine then slowly turn it the whitelist off until it still works.