Echo was able to turn on our lights, etc. before dinner, but after dinner Echo could no longer control any Smarthome devices, and was unable to "discover" any devices. Echo still could play music, and Echo specific skills.
There was no power outage, or configuration changes on our end. Our devices were all accessible via the Smarthome App and our remotes.
Reconnecting to the Smarthome took some experimentation (not just power down) and we lost Smarthome skill info (the groups we defined).
So this was a pain, and we do not know what happened.
Could be a software update was the culprit but unfortunately we do not know what the software versions were prior to the problem. Current s/w version shown is: 564186420 (no idea how this fits with Amazon's published version on their Update page).