What about physical water on the inside of the tent. With plenty of air flow that should go away?
Oh shit had a look at that 2nd pic in your OP, thats wet! Big difference between humidity and 'Saturation' I suppose. Sorry I should have looked.
I've never had visible water and its sat at 90% for extended periods during a storm etc.. I suppose its very condition specific too. Southern Hemisphere summer here. Im drawing from outside into a heavily insulated 1300mm x 700mm grow room built in a small garden shed, and exhausting into same vented garden shed.
While ive never grown in (or barely ever seen) a basement, lol. I'd imagine drawing and expelling into the same barely ventilated humid damp space is asking for trouble and your whole problem.
My exhaust system is replacing the rooms air with fresh outside air almost 24/7. The 3 x 300mm box fans running on the same timer blow the shit out of everything, but gently, lol. Needs to be pretty extreme wind to cause damage, so dont be put off by hurting the girls. Everything turns off for 15 mins every 4 hours atm.
I use temp and humidity controllers for exhausting and heating during winter but found during summer its better running almost 24 hours a day on a simple analogue timer.
If you cant control those basement conditions, can you draw from and exhaust elsewhere, using ducting? That site is a prime candidate for mould.