One thing to look at here.
Make sure the pistol and magazine are empty.
Insert the empty magazine and pull the slide to the rear till it locks back.
Take a look at the left side of the frame. Is the slide stop all the way up? Can you push it up higher in the notch in the slide?
If you remove the magazine, push the slide back to line up the notch in the slide and the slide lock and use a finger/thumb to push the slide lock up fully into the notch. Does the slide lock go upwards farther that way than with the empty magazine?
At the range do you see a difference between when the empty magazine locks the slide back and when you manually lock it back with a finger/thumb pressure on the slide lock?
Could be weak springs in the magazines. Could be the interaction between the follower in the magazine and the slide lock where it sticks through the frame to make contact with the magazine follower.
We've seen members report they have a magazine that won't even push the slide lock up far enough to catch the slide. Sometimes it's the follower not even making proper contact with the slide lock at all. Not all followers and slide locks are made the same, look the same or work the same.
