Years ago I too did the witness mark setup. At the time the mass majority of sheeple insisted the bolts had worked loose causing these problems.
Being concerned as you are to the incompetence of the dealer that installed the pulley, you might recheck the bolt is properly tightened. I would speculate that the shop merely zipped it on with an impact gun, never bothering to get the torque wrench. Even if they do, no assurance the torque wrench is accurate.
As flat rate workers, some may do a great job, while many would likely simply wipe those gearbox splines and not bother to remove the oxide particles which is the abrasive element. Those gearbox splines need to be very clean, same with the pulley, then fully coat both with the lubricant.
I can hear it now, bike on lift, zip bolt out with impact gun, with rear wheel raised walk belt off rear pulley, remove old pulley, install new pulley, zip bolt in snug, reinstall belt by walking it back on to rear pulley, set rear tire on ground, fully zip new bolt tight. Done. Simple and flat rate fast. Paying customer is not wise to any of it, the pulley lasts well beyond any local dealers window of warranty liability.
Repeat at the next sign of red dust.