I have Philips Hue with Smart Bulbs throughout my home. Majority of commands for lights are given through my Sonos One's and Beam. I have a lamp on one of two night stands in bedroom that was not responding to commands. Checked the Alexa app and it showed "Light unresponsive".
Quick Fix was to remove/re-install the bulb. Took all of a minute and everything was back to normal. Commands through Sonos One worked. As I said this is a quick fix and doesn't rule out a defective bulb. It wasn't Wi-Fi as the light on the opposite night stand responded to commands (besides I run in Boost mode for Sonos). Just thought I'd share the experience.