Marine Cpl
.577 Tyrannosaur.
Mine does the same thing. I put the recoil spring in below the notch. After putting it back together and racking it a few times, it goes into the notch on its own. Sometimes though it is in the position you just described when I take it apart after firing it.Strange, i took mine apart just a little bit ago and the recoil spring assembly was actually sitting just above the notch that its suppised to sit in. Now i dont know if i knocked it during disassembly or not so i put it back and racked the slide vigorously about 20 times then disassembled and it was sitting where it is supposed to. I did this two times with no change.
There is nothing I can see from the pictures that are different than mine so I'm not sure why the recoil spring is hopping out of the little Notch, but I would contact Glock as you don't want your life to depend on a gun that is not functioning properly.
Nevertheless, I've never had a reliability issue.