I have two new Era100s and am having the same problem on both. I have never had this issue on my Sonos Ones.
Alexa is enabled on the speakers. When you say the command word, the Alexa chime plays so that should mean it's listening, but we only get a response around 25% of the time. This happens when the room is totally silent as well as when there is background noise. I have noticed the music already playing doesn't quieten when Alexa is listening, as it does with the Sonos Ones, so I wonder if the voice assistant can't pick up what we are saying.
Tried all the deregister/disable skill/reset fixes I can find, and moved speakers to different positions, and there's been no change. Any ideas anyone?