ASRock x399 Taichi usb 3.1 gen 2 slow transfer

If you caused this by changing a BIOS setting, then reset your BIOS settings. There's a "load defaults" setting in like every BIOS made in the last 20 years. I have the x399 fatal1ty and I'm pretty sure they use a very similar BIOS, and mine definitely has a load defaults option in the Exit section. If you can't find that, I guess you could just clear CMOS. Isn't there a clear CMOS button on the taichi? Turn off the PSU, unplug the PSU, hold down the clear CMOS button for 10-15 seconds, and turn everything back on. Everything should be reset. If that doesn't work I think re-flashing certain BIOS versions will revert all settings.