scathed, 99% of the time, this is a low battery. make him change the battery first.
(nothing has changed, was working now its just cycling not firing paint.)
The reason is because its a sear tripper, the added friction of the sear trip noid is the first thing to starve for power when the battery gets below half power.
(pull trigger, marker cocks and fails to shoot) as it cocks it forces the ball past the detent and can cause a roll out.
Other than battery or training mode. if the LPR is set too low, the back block never pushes far enough back to catch the hammer. (it would fail to load paint if this were the case so I doubt it.)
Can you manually pull the back block back and force the hammer to catch on the sear?
lastly, I hate to even mention because you said it was working then stopped, is the lug depth. I seriously doubt he adjusted it, so check the battery first. If thats not it, I'll tell you how to adjust the lug depth. (or you can check the sticky

)