SEN0546 outputs bad humidity data

I originally thought I was doing something wrong as I wouldn't get a humidity reading over 50% even after 45 minutes wrapped in a damp rage. It would go up to like 70-80 for 20-30 seconds when I removed the rag, then go back down again.

Luckily and also unfortunately I had bought 2 before I realized you cannot alter the address, I tried the other sensor and it works fine.  

Anyone had similar problems?  

Also there isn't any good documentation on how to use the heater in very high humidity environments.