The temperature is the same on both, 66°. So it seems like it should be measuring the humidity accurately as well. That is staying steady at 65%.
Which sounds very high to me, and not inconsistent with the calculations of Jackofall. If it were my house, I would be stuck with the same conclusion: there is a yet unidentified source of humidity that should be dealt with.
You may be able to mitigate some of the associated problems by insulation and moisture barriers and venting and better windows, but the humidity will remain, in my estimation. I would also expect it to get worse in the summer.
Until you can identify that source, I would be running a dehumidifier in the basement. Perhaps you can knock the levels down a bit. This cannot be good for your house and belongings.