Could be many things. This is a concept with a few moving parts so you will get a few seemingly unrelated suggestions.
I would suggest you try and apply some science/patience to the process.
You first need to figure out what happened. Please read as much as you care on the subject.
Once you have some facts to put together, you should be able to design a correcting protocol.
To paraphrase Ray, I'd say the environment outside the humidor (including seasonal fluctuations) is as much a factor as the conditions inside the humidor... nothing is an absolute - it all needs to be put in perspective to make sense.