@Portercolin 

Simple instructions. 

1. Power off Deco units;

2. Undo everything you done on hub2;

3. Restore your Internet connection to original setup: with hub2 and everything;

4. Verify you have Internet access;

5. Connect Main Deco to hub2 with short Ethernet cable and configure it. During configuration select connection type "Dynamic IP."

In that setup, Main Deco behaves just like any wired client, such as desktop PC. It should get IP address from hub 2 and also you should see Main Deco in Deco app as online and healthy. 

If you can get to that point successfully, reply here and I'll give you directions on how to proceed further.