M&P pro 9mm 2013 vintage, apex comp kit, kkm barrell. Apex kit mod has 5k rounds,kkm has 500 rounds. Shoots great. Cleaned gun, shot maybe 30 rounds and now the slide locks back on every round with multiple magazines and 2 people shooting it. Took apart nothing I could see wrong, EXCEPT the slide lock lever did not seem like it had a lot of tension on it, either up or down. Is there a spring or something broke/missing or what?????