Devices lose internet connectivity or slow down after an hour or two when connected to RAX120

Hello esteemed friends.

Two devices on my network, both wireless, invevitably slow down or disconnect from the internet when a few hours pass.

My desktop has a AX200 PCI adapter that I don't have a lot of confidence in. However it works great when I have either freshly turned on my pc or have just reset the network adapter. I can get full gigabit speeds over wifi which is cool. But, it eventually drops to about 100-200 mbps. It does this while still connected to 5GHz and the same channel (48). I have the router set to HT160.

My laptop, about a year old and with an 802.11ac chip, always loses internet connectivity while remaining connected to the router. 

Both of these issues are eliminated if I set the RAX120 back to HT80. But then I can't transfer files at a gigabit from my desktop elsewhere. I have a few other wifi devices that seem to stay connected no problem. But my desktop is the only ax device.

Any ideas? I assumed issues like this would resolve in firmware updates but there hasn't been one since April.