Cannot Verify Server Identity

I've been getting this on my iPhone for the last few weeks (maybe month or more). Below that is "The identity of "www.tripit.com" cannot be verified.". I use the TripIt app and have a tripit subscribed calendar in my Calendars app. I deleted the app and then redownloaded it and that didn't make it go away. I haven't deleted the subscribed calendar but the link is https and it's the same one that tripit currently offers for me to see my calendars.

Kind of weird. I know other people have been having issues with this verification but for other apps. The tripit app works fine as does the calendar subscription.

Oh, the popup comes up at random times in random places (not when I'm accessing the TripIt app or my calendar.

Thanks for any help!

– Drew