If you warm the tag slightly by holding it in your hand, does the temperature change a little bit only, or does it jump around like crazy? And humidity if you breath onto the tag?
I suppose you have tried ‘cold-booting’ the tag by removing the battery for a moment and then putting it back?
Actually… which exact firmware version are you using? The 2.x firmware uses ‘RAWv2’ (data format 5) which the ruuvi station app does not parse correctly yet I believe, at least not the one on play store