Roscosmos’ official statement claimed, “Due to a short-term software failure, a direct command was mistakenly implemented to turn on the module’s engines for withdrawal, which led to some modification of the orientation of the complex as a whole.”
Sounds very much like a software glitch. But the head of Roscosmos, Dmitry Rogozin, later acknowledged someone on the ground may have made an error. “Everything was going well, but there was a human factor,” he told a Russian publication, as reported by Reuters. “There was some euphoria (after the successful docking), everybody got relaxed.”
This is the third major problem in less than three years that appears to be caused by Russian human error.
A Roscosmos launch in October 2018, had to be aborted after a Soyuz booster failure. Russian cosmonaut Aleksey Ovchinin and NASA astronaut Nick Hague had to make an emergency return to Earth. The investigation that followed revealed that a side-mounted booster had been improperly inserted into the core stage of the Soyuz rocket.