The PLS 8 carries three USB ports. Two are hosts, one is a device port.
The device port is for Judahs Studio, firmware updates and USB-MIDI to a computer.
The two host ports drive USB-MIDI devices directly, with no computer in the chain. IK Multimedia ToneX One units connect here as well.
Host ports supply power to what they drive, so a bus-powered device does not need a separate supply. A device with its own supply is unaffected.
If a USB device is not recognised, write down the device, the port it was in, and whether it was powered from the unit or from its own supply. That set of facts is what makes the report reproducible.