I have the same problem. I've been on the line with Honeywell for hours (different technicians) and all that they can guess at this point is that there's something in the router configuration that doesn't work with their connection or security standards. They are two new Honeywell thermostats and neither are connecting, which is why they do not see it as a Honeywell equipment problem.
They have provided me with specs (attached) and I understand only part of them (that we're connecting to the 2.4 ghz broadcast, and our password is alpha numeric.) I don't know how to determine whether the others are aligned, and if not, what can be done about that. Our local comcast technician says that he can't confirm the other settings. Our comcast system is in a new house, set up just about a year ago; we never tried to connect to the Honeywell thermostats previously, but will be away for several weeks and want to be able to monitor the heat while away, in case there's trouble.
I've attached the Honeywell specs. Is there some way to get help on this?
I'm having this exact problem. Several hours of tech support with Honeywell and Comcast. We did establish one checkpoint: If you set your iPhone to "personal hotspot" and use that to connect to the Honeywell thermostat, it works. This means the problem is the Comcast router, since the thermostant can connect to a wifi network. My error message says the connect was lost on Jan. 27, 2018. It's looking like Comcast changed the router settings sometime early this year or late last year.
Hours and hours of pulling the thermostat off the wall, changing the channels to 39 and 0, entering the wifi password, nothing works at getting the thermostat to connect to the router. It just delivers error code "049." Insanely frustrating. Will try to get a Honeywell technician to come to the home, but otherwise will deinstall the Honeywell unit and switch to a Nest or similar.
Wow what lousy documentation there Honeywell....
Under #5 you mention two protocols that are NOT supported.
Then in the next section those two same protocols ARE supported.