Longterm stress could certainly explain what had happened to the first crew members, however; it was only a short while after the arrival of the second crew that the angels revealed themselves again. How could the second crew be suffering from the stress of long term space travel as they had just arrived. No viable explanation has been offered as to why the second sighting occurred.
All six astronauts reported seeing "a smiling angel." The incident could be attributed to the the fatigue over a long space voyage, if it were only about the first crew. However, this explanation does not fit for the second crew -- a meeting with the angels took place shortly after their arrival at the station. So the second crew just confirmed the observation of the Angels.
The six cosmonauts who looked out the portholes all reported seeing seven angels all resembling humans but with wings. Each angel was reported to have been as big as a jet airliner and each of them had a smile of their face as if trying to share some kind of knowledgeable secret with the cosmonauts. Again keeping up with the movements and speed of the space station for a short while they later just simply disappeared.
The cosmonauts reassured themselves that they had gone temporarily insane and had experienced a group hallucination that was the only sensible explanation of what happened.
Incredibly they reported seeing the faces of seven angels who were hovering just outside the space station. They told ground control their faces and bodies looked human but these beings had wings and misty-like halos. The angels kept up with the movement and speed of the space station for 10 minutes before disappearing as quickly as they had come.
For a short time, the light was so brilliant it blinded the astronauts. Not knowing what happened, when their vision returned, each of them looked out the spacecraft windows for the cause of the blinding light.