App Security Code Texts Not Coming Through

I just moved from AT&T to Xfinity Mobile (iPhone) - since I activated late last week, I noticed that some sites/apps that require you to enter a text code - those texts are no longer coming through. And I'm having to use a different method (email or phone).

All personal texts work great, it just seems like something is blocking these certain "numbers" from texting me. Has anyone else ever run into this?