I reverted to earlier version of software (2.0.9.133) and still have the problem with Amazon Echo.
I just removed the Amazon Echo Skill App and installed the Amazon Echo App and now it works. So basically I reverted back to Hubitat version 2.0.9.133 then installed the Amazon Echo App to get rid of the Echo response of "device not responding" anomaly. So it looks to me that the problem is on the Hubitat side. Staff comments???
I’m not suggesting it could not be something in the HE side, but the Amazon Echo Skills app is going through Amazon’s API, so it must have a stable connection to their cloud to get device status. Local devices status is something Google is just beginning to implement across the board. Amazon does not have this as part of their API yet.
The Amazon Echo App is a Hue Bridge emulator, so it can locally control devices. So there’s an intermittent cloud issue with the Amazon Echo Skills app, but there is not sufficient evidence where that issue starts.
Something I didn't immediately realize: When I removed the Echo App, and installed the Skill, all my devices (as they appear in Alexa) were duplicated -- 2 of everything -- one of which was 'Offline' (presumably the old one), one of which was new. As a test I removed one of the old devices, then asked Alexa to turn it on - hey presto! No "device not responding". So I asked Alexa to forget all the devices, rediscovered them - and things started working.