This morning I tried to turn off an Iris plug via Alexa but she said it couldn't be found. I could control the plug from the HE device page and I could control it from the Alexa mobile app, but voice control still would't work. I went through device discovery with the Alexa mobile app-no dice. On a whim, I went into the HE's Echo app and deselected the plug,saved, discovered devices again with the mobile app, and to my surprise the plug was still there- and now voice control worked! I selected the plug in the HE echo app and it still worked.
I don't know why it wasn't controllable or how my actions fixed it. Just wanted to document it in case someone else runs into the same thing.