Some ISPs block inbound ports like port 80 and others. Since you are on various networks, HOME INTERNET PLANS are not a solid solution when you need to put up a server.
This riles those that want to put up a server without going to a business plan and is troublesome as you may have to find the network or ISP that is dropping the link or packets.
As to the DNS, be sure to use NSLOOKUP and in NSLOOKUP change DNS to test if the DNS is resolving or not. How to do that is on the web so I'll pause here.
I can access my home servers from the Internet from most locations. My ISP is Comcast. I've come across 2 locations that I cannot connect from: Two different's homes that both happen to have Comcast as their ISP.
Fails by IP as well as hostname. The correct IP is being resolved by DNS. Ping fails. Traceroute dies after the first hop. (their routers) My router and servers are not blocking or filtering by any IP or IP ranges. (wouldn't explain the traceroute result anyway)
Testing with my laptop and phone. (Cellular data always works.) Using their wifi but connecting to my VPN provider works on both devices. (different gateway)