Unusual fast moving object overtaking ISS

This evening, Dec 10th, 2019, I was observing the track of the ISS over Omaha, Nebraska from 5:36 pm local time to 5:42 local time.  The ISS track was from the northwest to the southeast.
 As the ISS came to a point high in the sky, I observed another object overtake the ISS, and nearly on the same path as the ISS.  The object was moving across the sky much faster (perhaps 5 times faster, or even more) than the ISS.  It passed the ISS within a degree or two about when the ISS was overhead, and continued on to the southeast.
 The object did not maintain a constant brightness, rather it became visible for perhaps 3 or 4 seconds and then faded out for several seconds, but on a repeating and consistent basis, as if it were tumbling.  It appeared to be a point source and did not have lights (strobes, rotating beacon, navigation lights, etc.)  that would be representative of an aircraft.