It seems a little sloppy compared to my g35 but there is some spring tension.Page 39 of your owner's manual.
9. SLIDE STOP LEVER TEST. Pull upward on the slide stop lever and release. The lever should snap down sharply into the frame. If the lever is sluggish, or remains in the upward position, refer the pistol to GLOCK, Inc. or a GLOCK-certified Armorer.
Two weeks ago I was SO for an IDPA stage and a shooter had the same symptom. Every round slide locked back. After 5 rounds he stopped. Unload and show clear. He left took it apart and stated the slide stop was installed incorrectly and it was fine the rest of the day. My money is on that.
I don't see the spring at the top of the slide stop lever. Can you take the same picture but with the grip of the pistol pulled more to you? Like you are looking toward the muzzle of the pistol but keep the slide stop lever in the shot.a picture of the lever if this helps