It’s look like we were late to the party!
https://community.home-assistant.io/t/emulated-hue-suddenly-stopped-working-with-echo-dot-v2
Changing Emulated Hue to work on port 80 (if possible) is a current workaround.
This worked for me. I’m still getting error messages on a couple of things (switches, specifically), and switches and a couple of my scripts don’t get triggered correctly from Alexa, but I can do most things through Alexa again.
From posts on that other thread, it looks like this is an issue on Amazon’s end caused by a firmware update, and they are working to fix it. So it may not be worth getting too deep into trying to fix it from the HA side.