uln2003a: Switching ground of device works, however, optional USB function of device doesn't work correctly
Take a look at the graph "6.14 Typical Characteristics" in the ULN2003 datasheet.
Even with only a small amount of current the output is still at least 0.7V above ground.
That means that your device's USB signalling is all going to be (at best) shifted 0.7V higher than it's supposed to be (could be even worse) - making the USB host in your PC very unhappy.