I don't have this gun, but I will try...
What you're describing sounds like your elevator/lifter is not returning to the down position to catch the next shell that comes out of the magazine. Is that right?

Take the trigger/elevator assembly out of the gun to diagnose the problem. I am assuming they come out as one assembly but, like I said I don't own this gun...refer to a manual otherwise. Often times, problems like this aren't hard to figure out. You just can't be afraid to take things apart. It might be as simple as lubricating the pin that it pivots on and working it back and forth until it smoothes out. Maybe you'll have to take the lifter off and inspect the spring and pin, perhaps replace the spring, perhaps polish the pin...you'll figger it out! If it was mine, I would take it apart, as lubricating is probably just a bandaid if its dirty or rusted. But hey, sometimes that's all it takes.