the quick fill fitting, cant get on get off
magazines need filing to align with the action, pellet probe and barrel
barrels wont fit back when removed, too tight
brass bits end of barrel deform too easily, the v notch
the knurled screw holding the barrel unscrews
pellet probe screw breaking, pellet probes blowback, dont lower the stock or it will hurt your shoulder or worse.
the o rings in regulator adjustment fail often
10 other o rings will fail randomly
pellets spiral almost from all barrels
fx cant keep up with demand so run machines with blunt tools, poor finishing
gauges off by a lot
the cam on the power adjuster wears, also its travel set screw needs locktighting not holding position.

who can add more? some of these were addressed. maybe

i wanted one too.
there is a good video from air fective when the guy talks about how to finetune shot to shot variation etc.