The ejector spring, or the ejector itself might be broke. I had one when i first started to shoot and sometimes it would eject, sometimes not, then one day it just quit. We took it apart and found that the ejector had cracked into two pieces. If i remember right, you push the ejector forward and remove a little round pin to take it out. Take a look
Being intermittent, your problem is probablt the ejector trip rod. This is the small diameter rod along the left side of the receiver.
This rod needs a little resistance in the receiver. If it doesn't, it can slide back into the receiver and not trip the ejector sear.
Pull the stock off the receiver. Have the hammer in the cocked position. Grab the rod and see if it slides in the receiver freely. You may be able just to tip the receiver up and watch it fall against the mainspring plunger. It shouldn't feel loose or flost around freely.
A little test you can try before removing the stock is to rest the muzzle on the carpet(UNLOADED of course), and dry-fire it and then open it. It will usually work everytime. Now point the muzzle straight up and dry fire it. Keeping the muzzle pointing up, open the gun and see if the ejector trips.
If any of the above show the gun not ejecting, pull the trip rod from the gun and put a slight bend in the middle. You don't need very much, just enough to feel in drag in the hole.
One other thing you can check when the stock is off, is the little round button soldered to the trip rod. This button helps keep the rod in the proper location, by fitting into a corresponding slot in the receiver.
I guess I should have given a little more detail. The shells don't stick at all, if they don't eject you can easily pull them out. It also acts the same way with Snap Caps or emptys, it will eject 10 times in a row then not eject, then eject the next few. Now it just stopped ejecting all together. I don't see anything broken. Is it possible there is some sort of a timming issue? I don't mind taking the gun apart, I just need to be pointed in the right direction before I start.