If your recoil spring happens to deflect off the recess cut in the barrel it's supposed to rest on that can cause the slide to get stuck when you try racking it back after reassembly . Just to make sure I'm on your page are you having trouble getting slide completely on the lower? Is it going on the lower but not cycling back? Is it cycling back and getting stuck on the slide rebound forward when you let go of it with your hand? Be as specific as possible. You said your sure it's gen 5 slide. It could be an issue of mismatched generations cause most of the printed lowers are designed with gen3 parts in mind. Time to go hang out at the gun store or whatever sporting goods store that has the best ammo deals and make friends with someone that also has a 9mm Glock (anything but g43) and start switching out one part at a time until you get a functioning firearm.