Is Alexa added in blacklist? Other than that, I could not think of other reasons. Or it could be settings on the Alexa. Double NAT issue is quite common on Xbox or PS. That happens if you have two...

Do you need VLAN ID for internet access? I heard that it's required for fiber connection. One way to verify is connect a pc directly to the fiber box, if you can access internet, then no VLAN ID...

How about using WAN IP address to login? Do you have public WAN IP address? And verify if ddns is successful by using nslookup command