This happens to us almost every time, on the SAME pillar, so we move the laser and knock the pillar down first ourselves so as to not waste a shot at using it.
From what I remember, if you are on the laser facing the Titan spawn point, it is the third pillar forward on the right side.
Every time I run the Titan, I make sure to take out that pillar as the 5th one, and the 4th one forward last. The first 4 times I ran that quest, I took out 4r 5th, and the laser shot destroyed 3r. Ever since I started using 3r before 4r, no problems.