One of my Ruuvi sensors has a blinking red light and disconnects from the Ruuvi app and then re-connect again after a few seconds. I have tried to update firmware, but it turns out to be impossible. I have removed battery, same result. The app (in my iPhone) receives messurements from the sensor. When I use the same app in my iPad, there is no messurements from that sensor (the other two works well).
Most common cause for this kind of behavior is a faulty battery. Please try to use the tag with another battery. If that does not help please send good-quality pictures of tag circuit board. Sometimes there is visible damage or corrosion in the circuit.
Wow, it was the battery!
I put in a new battery and everything is great again.
Thanks a lot for your help.