bruce
5
As the mentioned 'On PC works great' this time the PC is connected the router via the cable?
Probably the USB3.0 port interfere the WiFi speed, but only affect 2.4GHz, not 5GHz.
Further check:
- without the USB drive, how many the WiFi speed in the PC/phone and does the speed ok? speedtest.net
- with the USB drive, how many the WiFi speed?
- with the USB drive, is the phone or PC connected to 5GHz WiFi of the router?