Hmmm... When I turn the thermostat Heating On/Off the Setpoint remains the same, in my case 18 degrees.

EDIT: I'm wrong, here exactly the same: It changes my setpoint to 5 degrees!

But my log shows the error you provided us a lot:
2018-10-09 11:43:52.404 Error: Honeywell: Error getting thermostat ...

Since the latest release of Domoticz v 4.9700 the Honeywell Lyric is implemented( view topic "Domoticz version 4.9700 released (Stable)": https://www.domoticz.com/forum/viewtopic.php?f=3&t=23948 ). The posts of @marcoschaap are seeming to confirm this (but it's on a beta release).

Anyone ...