DuckDns with Hass.io makes Alexa really slow

I setup DuckDns last night and got it working with Hass.io and configurator but almost immediately Alexa started responding really slow and sometimes would say not responding. As soon as I reverted to not use DuckDns my speed is fine again.

Does this have something to do with port forwarding 443 to 8123 on the hass.io pi?

I also have this problem. It seems to be related to DNS resolution with DuckDns, because only the first request (when the lambda is launched) to Alexa is slow.
I’ve also setup a ping sensor a while ago and noticed that if I ping the hostname it would sometimes fail, but it would never fail when I ping the IP address directly.