Dear...
if you have issue on MT6000 with 2.4ghz and usb 3.0 device can you please try this command:
echo 1 > /sys/bus/usb/devices/usb2/2-0:1.0/usb2-port1/disable
should force use usb as 2.0...
to revert to usb 3.0
echo 0 > /sys/bus/usb/devices/usb2/2-0:1.0/usb2-port1/disable
If it is ok I'll try to add this setting on Luci.
Thanks