(For clarity: I know that what I'm "suggesting" here is actually a bad idea, and that the solution to this problem involves a shitton of Cat6 cable.)
My Wi-Fi adapter really needs a "force 802.11ac and also crank transmission power up illegally high" mode on it, lmfao. Because sometimes, it's just like "lol fuck you going to drop down to 802.11n specifically when you're trying to transfer over a terabyte of data".
I give up. I'm just doing this directly via Ethernet, which just means moving the smaller device closer to the larger one.
Sometimes I wonder if the accepted solution to computers is damaging your landlord's property and installing extra speedy/spicy 20 foot wires under all your flooring.