Cannot verify server identity - Apple Configuration Profile Generator iOS 14

Hi all,

I’ve setup nextdns using the profile configuration on my iPhone and iPad. Everything worked fine until recently where I often get this pop up on my iPad (as attached). I’m not sure what went wrong and I’m not sure how to troubleshoot this error. It’ll appear sometimes throughout the day. 
 

Any help? Sorry I’m not that tech savvy. 
 

imran