Thanks Ali Raza for your inputs.
As a first step, we did all what you have recommended to see if the line had some design issues. But line is perfectly safe in design (and as-built) condition.
Dave, yes some transient loading was there, which broke two axial stops and moved the line horizontally so much that the line fell from shoes. Now it is hanging from its end points (the points where supports are as per intended design.) The line is resting on two of the supports with pipe bottom touching the beam top and at three location it is showing sag and is not touching the beam. Still lifted.
When the transient force was there, the line moved horizontally at the +Y support locations and when shoe bottom moved away from beam, it was like pipe is 150mm away from supports, so it bent down (fell) due to gravity and is now resting on two of these supports as stated earlier.
This is the reason for the modeling +Y supports with 150mm gap.
Dave, good point about Y supports acting as line stops is interesting and logical. This may be happening now.