I had similar problems with my Heatits. All 7 was loosing connection over a week.
For me this worked:
My 7 Heatit TRM2fx all lost connection with the Homey within 36h.
The solution was to change the parameters:
Temperature report interval (s) from default 60 to 3600
Meter report interval(s) from 60 to 32000
My conclusion is that the frequent communication of the Heatits overloaded the z wave net sometimes.