SRT 321 disappeared from Devices

Hello there,
I have just embarked on my z-wave journey and installed the srt321 thermostat and receiver. They appear to be working ok albeit the srt321 does not update the vera 3 dashboard on a regular basis. My question is this, if I may; I created a Schedule and Scene for the thermostat yesterday evening. Upon doing this the SRT321 (_Horstmann Radiator) disappeared from the Dashboard & Devices. Lo and behold it has reappeared this morning. I am somewhat concerned. Would anyone have an idea as to what might be happening?