Those parts don't just break, Al. I am betting that the tech that installed the injectors recently didn't seat the injector properly in the cup.
That's a Hino, right? Toyota engine?
Those injectors, from what I remember, are "direct" injectors that snap into the cups below the rocker assembly. That are held down with an 8mm (?) bolt and hold down. There's minimal vibration involved because that are a stabilized unit with an O-ring seal into the cup.
If the new injector wasn't seating properly into the cup and the tech "forced" it down with the holddown, that would cause your broken tip.
Were the cups replaced as well?
Either way, it is definitely on the previous shop that installed the injectors, though they will probably fight that warranty repair tooth and nail.