The red line on the X Pole can show if the ceiling height is measured incorrectly, especially if your ceiling height is right at 9ft tall.
Even within the same room the ceiling height can vary and some people measure against the wall for convenience. By doing this it might be measuring a lower ceiling portion or a higher one as the height can shift even within the same room.
If you are installing on carpet, carpet compresses causing the ceiling height to be taller than 9ft and can require a longer pole in order to be installed safely.
Another thing that it could be is the ceiling stud/joist is settling and can be pushed up a bit when expanding the pole.
All of this can vary and add a mm or two to the height difference.
If this has happened to you, in most cases, a 200mm extension can fix the issue.