The groove is there for assembly purposes. Once the gun is assembled and the slide is cycled once, the rear of the recoil spring assembly moves down slightly although it usually doesn't move down so far that it's completely out of the groove after disassembly.Basically when I field stripped the gun the spring was extremely loose almost falling out. Not even in the groove at all.
The fact that the recoil spring assembly is completely out of the assembly groove upon disassembly is unusual but it does not indicate any sort of a problem and should have no effect at all on function.