Does the hammer have a "V" or "U" notch cut thru the front or side of the material that surrounds the cap?
Some hammers don't.
The notch is intended to allow the gasses to vent away from the shooter but it also serves as something to break the wall of the spent cap.
This usually, but not always keeps the spent cap shell from lodging in the hammer recess.
Glad it is better. Sometimes changing to a 'hot shot' type nipple will solve it also. I have a similar problem with my wife's rifle and will be both hot shotting and notching to try to resolve.