Knowing that the Russian space program has bee rife with failures over the years, my guess would be that the 5th object is something that wasn’t intended to go into orbit with the satellites. Like a piece of the satellite container or a chunk of rocket motor, etc.
What space program isn’t rife with failures? It’s the nature of the beast when dealing with non-mature technologies. It’s not like the US space program looks very good right now, when we need to rely on them to put things in orbit.