I built a website in Shopify, see it here: practicalamerican.com
The site loads fine on desktop, mobile, wifi, every carrier - except AT&T. In the later case, the browser gives an error that there is no internet connection. Presumably, it never receives a response from the server, so it makes that determination.
Loading any other site works fine. I've confirmed this on multiple devices and multiple browsers, Android and iPhone. Weirdly, if I toggle Wifi on my iPhone and load the page, then toggle Wifi off and try to reload the page, it loads fine. Perhaps some sort of browser caching? Not sure how it would determine it has an internet connection as per the previous point.
I've tried: adding
<meta http-equiv="Cache-Control" content="no-transform">
The issue cleared about 72 hours after it started. That seems consistent with DNS caching, as suggested by Ira. The other proof is that when the page was loaded on Wifi, I could then reload it on LTE, but I could not load it on LTE in an empty browser tab.