Hey Nick,
I remember having this issue earlier this year when the heating was on. We've just switched the heating back on again (last weekend) and have noticed that I need to keep restarting the plugin, as otherwise it doesn't actually update or work.
Currently all of the TRV's are reporting as last updated 14th Oct at 10pm with the Thermostat itself reporting as being on - except the thermostat is currently Off and none of the TRV's are reporting the right temperature.
This also prevents the set mode action from working - so my Home / Away settings within Indigo aren't enabling or disabling the Honeywell system either.
I'm on v0.4.6.
Any ideas?