Why is the Nest's indoor humidity lower than other sensors?

My Nest is consistently showing a lower humidity than my other sensors, and I don't understand why. The temperature readings are correct between my Nest and the other sensors, but the humidity readings are not matching up with the Nest and my other sensors. I read somewhere that the opening behind the Nest should be closed off so I stuck a bunch of insulation behind the Nest opening. It didn't help any. I have a reading from my other sensors, and it says the room is 55% humidity, but the Nest says it was only 52% humidity. I have a whole house dehumidifier, and I told the Nest to turn on since it wasn't going to turn on by itself (I had the humidity set at 55% and told the Nest to turn on if it reached that level), and shortly after 5 minutes of it being on, the Nest humidity dropped from 52% to 49%. Something isn't right with the humidity reading. Has anyone else had issues with the humidity reading? Is there a fix to this problem?