iPhone/iPad: Cannot Verify Server Identity: version.taxcut.com

I am seeing this error message on my iPhone and iPad multiple times per day, usually right after unlocking my device:

Cannot Verify Server Identity

The identity of "version.taxcut.com"

cannot be verified. Review the

certificate details to continue.

Interestingly, it does not show up on my iMac.

I don't have taxcut installed on my iPhone, iPad or iMac, nor any other H&R Block software (I have used Taxcut in the past but not within the last eight or nine years, and not on any of my current devices). The certificate is an Akamai certificate. When I was in the Apple store recently to pick up a new iPad, I asked about this. His preliminary examination suggested to him that it was tied to the AirBnB app. I've deleted that app but the problem continues.

How do I get this to stop popping up or at least trace which app is causing this so I can delete it?