The data regarding the Nov. 30, 2018 launch from Plesetsk Cosmodrome on Space-Track.org at the time of writing.
But there is also the distinct possibility that this could be yet another so-called "inspector satellite." More on that later, but we've actually seen almost exactly the same thing happen at least once before.
The five objects that the U.S. military tracked after Russia's launch of three Rodnik communications satellites on May 23, 2014. It is noteworthy that in this case the inspector satellite Kosmos-2499, also shared the same perigee as the upper stage.
The video below shows a concept the U.S. Defense Advanced Research Projects Agency has been working on regarding an advanced inspector-type satellite called a Robotic Serving Vehicle (RSV).
In addition, their diminutive size could make them hard to track, especially if they hid next to their target, lying in wait, or blended in with the extensive amount of "space junk" floating about the Earth's atmosphere. The ability for even smaller satellites to act as motherships for even tinier systems, as was apparently the case with Kosmos-2519, -2521, and -2523, could make it even harder to judge exactly what "inspector" capabilities an opponent may actually have in orbit. Inspector satellites have also generally been small enough for the Russians to include unannounced in other launches in the past.
The Kremlin has categorically denied that any of these satellites, which it calls "space apparatus inspectors," are weapons. Most recently, the Russians denounced concerns that Yleem Poblete, the U.S. Assistant Secretary of State for Arms Control, Verification, and Compliance, raised in August 2018 about the purpose of Kosmos-2519 and its associated sub-satellites as "unfounded, slanderous accusations based on suspicions." The Russian government, however, has not provided any hard evidence to support their insistence that the satellites are entirely non-threatening.
But it is also clear that the Russians have an active and multi-faceted anti-satellite weapons program. In September 2018, The War Zone was first to reporton the emergence of a new, air-launched anti-satellite interceptor and a specially modified MiG-31 Foxhound fighter jet to carry it. Russia also has ground-based interceptors that could engage satellites and claims to be working on airborne laser systems that may be able to blind or damage the optics on spy and early-warning satellites.
A MiG-31, in the foreground, carries what appears to be an air-launched anti-satellite interceptor during a test flight in September 2018.
On top of that, space-based weapons present unique challenges for the international community, especially since neither the United States nor Russia has so far been able to articulate the exact threshold for what would constitute a conflict in space. The U.S. government also opposed treaties that have been proposed so far to limit space-based weapons, arguing that the language is vague and unenforceable and the terms are unverifiable. Dual-use systems that have legitimate non-weapon functionality, such as inspector satellites, don't help efforts to try and firmly establish these definitions.
In the meantime, Russia doesn't appear to be slowing down the development and expansion of its anti-satellite capabilities. As part of that push, it may very well have just added to its constellation of possible "killer satellites."