Failure to go into battery?

To keep this short and simple I have a used C9-A2. Whenever I go to chamber a round via dropping the slide to go about my day concealed carrying the round always chambers fine. However during a range session, after a few mags, when I drop the slide to chamber a round it fails to go into battery and will either sit ever so slightly out of battery or just a few cm out of battery, and after that range session I noticed that it has the same issue. However, after trying to chamber a round repeatedly it would fully go into battery every now and then. Dont know whats causing this and its a mildly annoying issue if I'm being honest.