UFH-newB

I have a new build house with ground floor wet Heatmiser UFH. Over the past year I have noticed that in summer, an indicated Neostat V2 room temperature of 19C of higher feels very comfortable in a short sleeved shirt. However in winter, the same indicated temperature, 19C, feels cold enough to need to put a jumper on. So I took separate temperature measurements from summer onward. On a warm day the Neostat temperature and the measure temperature were the same, +- 1/2Deg C. However now, with an indicated Neostat room temperature of 19C, an independent measurement in the room shows anything between 16C and 18C. The only way I can get the temperatures to agree again is to manually turn on the UFH in that room, or crank the Neostat setting up to 20C or 21C, wait until the room catches up a couple of hours later, then turn the setting back down again. Is this sort of behaviour typical, and if so, can it be avoided in some way?