Glock 20 Question in Connector
 

I have a glock 20 I just bought used. I tried to put a new 3.5 connector that I have had in several of my other glocks so I know it's not the connector. I put it in, and wouldn't fire so I thought. I took apart and put it back in several times, and it wouldn't fire, which led me to taking my glock back apart the long way several times. Last time I took it apart and reinstalled it, and put it together still wouldn't fire. Frustrated, I shook it in my hand and click. Thats right, shaking it made it fire. So what is the deal? What does that mean? Thanks in Advance.