Never experienced something like this with any build. I have a rig running a ROG STRIX Z370-I GAMING motherboard. All USB 2.0 ports on the motherboard backpanel, and one USB 3.0 port on the motherboard backpanel (located next to a USB-C port) have stopped properly functioning. Behavior when a device is connected can best be described as a low voltage condition. Peripherals like mice and keyboards have noticeably dim LED's, and a webcam fails to be recognized as OK in device manager; The webcam is not usable. All peripherals I have tested *only* function properly on two USB 3.0 ports on backpanel, and one USB 3.0 port connected to front panel header on the motherboard. I haven't a clue what's happened here. I have attached a screenshot that shows the location of the only functioning USB 3.0 ports on the motherboard; The lone chassis-mounted front panel USB 3.0 port is not pictured (of course). Looking for some help on how to proceed! I would think it's highly unlikely to have a hardware failure like this that leaves two ports unscathed.
View: https://imgur.com/a/CAju06N
View: https://imgur.com/a/CAju06N