Was the gun you sent in the same one you got back? I don't know how replacing the striker could cause failures to feed.

Did the gun jam while firing or only when you racked the first round in? Either is unacceptable but jamming while firing is a much more serious issue. I have had a couple of guns like a Kahr PM9 that were reliable when being fired but had issues when manually cycled. Frustrating at the range but I still trusted them for carry since I keep a round in the chamber. I eventually replaced the Kahr with a less finicky Glock 43. The older I get the less tolerance I have for picky or even slightly unreliable guns.

Too bad about the sight. The rear sight has to be removed to get at the spring for the firing pin block so I am guessing the factory took it off for that reason. But they did a really poor job when they put it back on.