Assuming you have the right caps and they are firmly seated. After you make your first try or you can deactivate a cap, check the print that your hammer face is leaving on the cap. You should be seeing at least a 50% print area. It's possible that your hammer face or bottom of the cup is not aligned or even touching the top of the nipple cone. Also, your spring may be weak but have never seen a coil spring do that, on these, unless someone messed with it. ....
Also, make sure you haven't stacked spent caps in your cup. ...
Be Safe !!!