hook the aTV back to ethernet, and reboot the aTV, HomePod and router.
if that doesn't help, make sure your wired and wireless devices can "associate". there is sometimes a setting in your router to prevent the 2 sides of your network from talking to each other (it's a safety feature, but not needed in most home environments). If this is set incorrectly you might also have run into problems using airplay or the remote app when trying to use your phone to send audio/control the a wired aTV.
Just re-read the original post, and since your Alexa and fireTV had the same issues, the associate issue might be the problem.
you're on a "normal" home network? not in a dorm or something like that?