I have the same problem. I had everything running fine, then got a new Echo today. The new Echo always reported all my items as not reachable, so I removed them and tried to add them again using the alexa app. The app does not find the things any more, even though it has worked with the same configuration without problems.
My Hue lights are discovered, so the Echo does not seem to have a hardware problem.
The log only shows two entries (with DEBUG level):
2017-11-24 17:39:00.283 [DEBUG] [ulation.internal.HueEmulationServlet] - 192.168.178.55: GET /api/description.xml
2017-11-24 17:39:00.333 [DEBUG] [ulation.internal.HueEmulationServlet] - 192.168.178.55: GET /api/description.xml