Sonoff TH16 with Si7021 sensor spontaneously switches on/off

Has anyone encountered the problem of the Sonoff Th16 unit with Si7021 sensor switching on/off on its own in temperature control mode - other modes I have not checked.
I have connected, fired up the eWelink and seemingly everything is OK but the controller has a sort of transient and can switch on/off for about 2 seconds and then it can be quiet for 30 minutes or two hours and the same thing happens again (random time intervals). I have no idea what this could be dictated by.
Maybe someone has an idea.