emonTH suddenly stopped reading temp and humidity

I’ve got an emonTH v1.5.2 setup on channel 19 that has been working fine since 2015. now since a week it has stopped working. it sends data as:
Temp = 1
Humidity = 0
Battery = 0
signal = -52
as soon as it’s connected to the battery and then nothing more.
the red led turns on steady and then blinks for a while as a sign there is a sensor problem. I changed the sensor with another sensor I have on another emonTH, but it still does the same and the other emonTH works fine with this sensor, so I would exclude the sensor.
before throwing it away, do you have any type of suggestion as to what could be wrong?
I already checked the traces of the sensor and all of them are ok (continuity).
I verified the voltages on the +3.3V line and it’s ok. the 5V is a little over 3, but it’s the same also on the other emonTH so I assume it’s ok.

any other idea?