Thanks NB for the capture file. I think this points out the issue but not the reason yet.
The LOCATION header from the AlarmDecoder WebApp needs to contain the full path to the xml file to describe the host. AFAIK this would be hard coded and when sent back to the HUB it will format a message that is sent to the cloud where this parameter is used to make more detailed requests of the device capabilities. Instead it just asks again in 4 seconds and then stops.
See here for example:
http://docs.smartthings.com/en/latest/c ... nager.htmlScreenshot from 2017-11-27 22-47-06.png
Will look over code in the AM to see where this response is done to a "discover" message.
Best
SM