With the pistol empty, slide closed ,no magazine , see if the slide stop lever is held down . It should have spring pressure down, but very light , just enough to keep it down. If that's the case then that isn't the issue. Are the magazines in those guns able to be disassembled ? I don't have one, so don't know , but if they can be taken apart , do so and give all parts and the body itself a good cleaning. Make sure the follower ( the follower is the part inside generally plastic in newer guns, that the bullets sit against )is coming all the way up to where it would contact the slide release lever and push it up.