Bernhard, running my RYZEN for some days and noticed that tha xhci issue also 
affected the USB keyboard and the USB mouse:


At this time, the system is allready running for 2 days:
Aug 24 08:38:41.665376 tux1 kernel: usb 1-12: new low-speed USB device number 19 using xhci_hcd
Aug 24 08:38:42.001609 tux1 kernel: usb 1-12: New USB device found, idVendor=046a, idProduct=0011, bcdDevice= 1.00
Aug 24 08:38:42.001850 tux1 kernel: usb 1-12: New USB device strings: Mfr=0, Product=0, SerialNumber=0
Aug 24 08:38:42.098291 tux1 kernel: hid-generic 0003:046A:0011.0003: input,hidraw0: USB HID v1.11 Keyboard [HID 046a:0011] on usb-0000:03:00.0-12/input0
Aug 24 08:38:43.631091 tux1 kernel: usb 1-12: input irq status -75 received
Aug 24 08:38:43.631384 tux1 kernel: usb usb1-port12: disabled by hub (EMI?), re-enabling...
Aug 24 08:38:43.631409 tux1 kernel: usb 1-12: USB disconnect, device number 19
Aug 24 08:38:44.025057 tux1 kernel: usb 1-12: new low-speed USB device number 20 using xhci_hcd
Aug 24 08:38:44.361600 tux1 kernel: usb 1-12: New USB device found, idVendor=046a, idProduct=0011, bcdDevice= 1.00
Aug 24 08:38:44.361839 tux1 kernel: usb 1-12: New USB device strings: Mfr=0, Product=0, SerialNumber=0
Aug 24 08:38:44.401604 tux1 kernel: input: HID 046a:0011 as /devices/pci0000:00/0000:00:01.3/0000:03:00.0/usb1/1-12/1-12:1.0/0003:046A:0011.0004/input/input18
Aug 24 08:38:44.458277 tux1 kernel: hid-generic 0003:046A:0011.0004: input,hidraw0: USB HID v1.11 Keyboard [HID 046a:0011] on usb-0000:03:00.0-12/input0
Aug 24 08:38:49.031776 tux1 kernel: usb 1-12: input irq status -75 received
Aug 24 08:38:49.032082 tux1 kernel: usb usb1-port12: disabled by hub (EMI?), re-enabling...
Aug 24 08:38:49.032099 tux1 kernel: usb 1-12: USB disconnect, device number 20
Aug 24 08:38:49.425365 tux1 kernel: usb 1-12: new low-speed USB device number 21 using xhci_hcd
Aug 24 08:39:04.905175 tux1 kernel: usb 1-12: device descriptor read/64, error -110
Aug 24 08:39:20.478280 tux1 kernel: usb 1-12: device descriptor read/64, error -110
Aug 24 08:39:20.774967 tux1 kernel: usb 1-12: new low-speed USB device number 22 using xhci_hcd
Aug 24 08:39:36.331757 tux1 kernel: usb 1-12: device descriptor read/64, error -110
Aug 24 08:39:51.838723 tux1 kernel: usb 1-12: device descriptor read/64, error -110
Aug 24 08:39:51.945370 tux1 kernel: usb usb1-port12: attempt power cycle
Aug 24 08:39:52.588394 tux1 kernel: usb 1-12: new low-speed USB device number 23 using xhci_hcd
Aug 24 08:39:57.415723 tux1 kernel: usb 1-12: Device not responding to setup address.
Aug 24 08:40:02.448295 tux1 kernel: usb 1-12: Device not responding to setup address.
Aug 24 08:40:02.655042 tux1 kernel: usb 1-12: device not accepting address 23, error -71
Aug 24 08:40:02.778269 tux1 kernel: usb 1-12: new low-speed USB device number 24 using xhci_hcd
Aug 24 08:40:07.604975 tux1 kernel: usb 1-12: Device not responding to setup address.
Aug 24 08:40:12.638751 tux1 kernel: usb 1-12: Device not responding to setup address.
Aug 24 08:40:12.845561 tux1 kernel: usb 1-12: device not accepting address 24, error -71
Aug 24 08:40:12.845696 tux1 kernel: usb usb1-port12: unable to enumerate USB device

At this time only hard power off will help.

I got rid of that and reverted the ugly xhci patch. Will now see if that will solve the xhci issue.