Soviet Secrets of Space

United States astronauts do not hold a monopoly on UFO sitings in space.

Soviet cosmonauts conceal truth about UFOs - Pravda

In 1991, Musa Manarov was observing the module with the new crew nearing the Mir Space Station, filming the process on video camera. He suddenly saw an antenna-like object separating from the module. He informed the cosmonauts inside the module that something had undocked from them. Nevertheless, it never became possible to identify the object, although it was filmed on camera.

One of a few stories in the article.

So what about tales of UFOs from astronauts and cosmonauts makes them more credible? These folks have a functional knowledge of flying craft. While uncle Jeb in the old hill country might mistake a midnight game of glow-in-the-dark frisbee for a close encounter, we can reasonable assume that space faring folk would know the difference. Those who are not well versed in flying craft will undoubtedly have a scientific background that will lead them to question their experiences.

There are relatively few astronauts and cosmonauts. The fact that even a handful of each claim to have spotted bizarre UFOs is everything but hard proof.