Profilux Terra humidity sensor works inverted now?

Hello all,

I've had a running Profilux II terra for 10+ years now and since last week I've noticed quite a bit of condensation on the windows. If I connect to my PC and get the readout I see that every night the humidity goes to 0% and goed up during the morning. I just checked what was happening directly after a 30 second misting cycle. The humidity drops down! It was 46% (not correct) and dropped down to 9% just after misting.
It could be the sensor is just worn out but a reversal seems so particular. I have not recently updated anything, had it connected at all nor tried anything in the settings on the device.

Is there any way to correct this?

Edit: after putting ventilation on maximum for a while I kept track of the himidity and noticed it kept "increasing" (actually decreasing) till it reached 58.9%. It fluctuated between 58.4 and 58.9 for a while and then started decreasing as it normally should. It's set to 45% and is holding as it normally does at 53% (10% hysteresis)...