Trigger reset issues with MPX-K

I recently got an MPX-K and I've been having trouble with the trigger.

Went through 43rds of 115gr without a hitch and then it started... It became a single shot pistol. I tried 124gr and 147gr, no luck. Same issue.

I am looking into getting anti-walk pins, or any other simple resolve for it. I wouldn't like to send it to Sign, but it's my last resort if I can't figure this out.

Anyone have a link for anti-walk pins for it? Or any ideas of what to check for in order to identify what the problem is?

Thank you in advance.