When FX3 SS Explorer kit is connected in USB Boot mode (J4 jumper in place) to a Host it enumerates as a Boot loader device which is 2.0
Please check if this is the problem. If yes, then you can program a (super speed) firmware into the EEPROM on SS Explorer kit, then remove the J4 jumper. This when connected to a Host enumerates as 3.0 device.
Yes, J4 is removed. The preprogrammed demo firmware enumerates at 3.0 speed--blue LED flashing quickly--when plugged into a USB port without the redriver, but the LED stays solid when the redriver board is used.