pressure regulator present? too much pressure can cause an issue

Chances are you did not have the nut rotated in the proper position before pushing the tubing on. The nut is supposed to be rotated all the way in(towards the center of the tee), to expose the maximum amount of the female portion that goes into the tubing. After you push the tubing all the way on (push and wiggle on as much as possible), then the nut is supposed to rotate outwards and squeeze the tubing between the rotating nut and the portion that is inside the tubing. This may be counterclockwise and not the typical righty tighty lefty loosey. I did it incorrectly before with a different brand.

If you did it correctly, just exchange it. It might just have enough of a defect to let it pop off.