IPhones work on WiFi but cannot resolve IP using ATT data network.

Does anybody had issues with iPhone and ATT using CNAME. We delegate wip.company.com to GTM and use CNAME for a website. It works with Android, Windows, Linux, etc., IPhones and Ipads work on WiFi but cannot resolve IP using ATT data network. Android on ATT works without issues. Is it Apple bug or I missed something in GTM settings? See dig example bellow

dig www.company.com
www.company.com.        3600    IN      CNAME   www.wip.company.com.
www.wip.company.com.    300     IN      A       200.200.200.200