Interesting.
I've never aged beef beyond the processor's usual 2 week hanging time.
You have much more experience than me, which is none. From looking at your Meal Planning post, it looks like you are mostly wet aging in vacuum packs? Maybe an occasional dry aging? And of course the dry brining brisket.
From my empirical experience, food left uncovered in the fridge tends to dry out, and modern refrigerators with defrost cycles have little visible condensation (maybe some along the coldest walls and vents). Remember 50% RH at 35F has much less water content than at 70F.
But I don't understand how opening the door could lower the moisture inside your fridge. Opening the door lets in warm air, which has a much higher moisture content, increasing likelihood of condensation and frosting. Opening the door also probably triggers the compressor, which should cause a sudden drop in RH due to the moisture frosting onto the coils. This might be what you are seeing. During the coil thawing cycle, frost on the coil collects into the drip pan and most evaporates into the room. However, some of the water vapor is released back into the fridge, and RH should then slowly increase. I think it would be better just to keep the door closed.
Have you considered using desiccants in your fridge, or maybe a small external vacuum pump (with a water trap)? A continuously running fan in the fridge should also help. Then again, if it ain't broke, don't fix it.