Odd HASSIO & DuckDNS connection problem

I hope this fine group can help shed some light on a problem I am having connecting from my HASSIO instance through duckdns.

My hassio is running on a raspberry pi 3. It is up to date and running stably.
I can connect through https://XXX.duckdns.org from the local network at my farm (where the pi is on the same network). I cannot connect from my home network (fiber connection with 18ms ping, 100mbps up and down) whether I am connecting through my wifi router or directly with ethernet connected to the router. I also cannot connect through my ATT cell phone or through the mobile hotspot of my ATT cell phone using my laptop. I CAN connect through my verizon mobile hotspot from my laptop.

When connected through my home network, I can ping the hassio pi (ping XXX.duckdns.org). The screen shows the home assistant logo and the spinning wheel with loading data. However, the home assistant screen never loads. It is the same behavior with my ATT cell phone.

Does this behavior sound familiar to anyone? Where should I start troubleshooting?

montyhp