Unable to access website via AT&T mobile 5G

Unable to access website via AT&T mobile 5G iphone.
Things I have tried:
Same iphone can access the site via wifi.
Same phone can access the site using a non-ATT DNS via the Trust DNS app.
Desktop Chrome browser using the iphone as a hotspot says “ERR_CONNECTION_RESET”.
Desktop with a different ISP works.
If I change the A record for the naked domain in Cloudflare to DNS-only (not proxied) and the WWW cname, the site is accessible.
This appears to be an issue with only AT&T 5G and Cloudflare as all other ISP options available to me work.

This appears to be resolved as mentioned in another thread Site not accessible from AT&T ceullar data