When using external usb3 hard discs you might receive the error:

[95971.770775] xhci_hcd 0000:00:14.0: xHCI xhci_drop_endpoint called with disabled ep ffff8800b951be80
[95971.770782] xhci_hcd 0000:00:14.0: xHCI xhci_drop_endpoint called with disabled ep ffff8800b951bec8

with Linux (3.16.0-4-amd64) and

[   41.238984] scsi 6:0:0:0: Device offlined - not ready after error recovery (auch rmmod xhci_hcd && modprobe xhci_hcd hat nichts gebracht).

with Linux 4.8. In both cases the disc is not recognized by the system.

This error only happened with some discs, but not with others.
(Using the same sata-usb3 bridge.)

It seems to be a timing issue which can be solved really
easily:

Simply give the hard disc some time to start up, and connect
it 10sec later to the computer.

Alternatively,

	# rmmod xhci_hcd && modprobe xhci_hcd

as root, also solves the issue.