It could simply be crud in the channel that the bolt runs in, or in the ejector rod, or even the front ejector rod latch. Could also be a kinked up spring.
Try operating the latch with the cylinder open, then get a flat object like the side of a standard screwdriver and push down on the cylinder latch rod where it protrudes thru the ejector star. This will help you focus on the problem. If you can compare them to known, smoothly functioning weapons it will give you an idea if the problem is one or the other or maybe both.
A seriously bent ejector rod or even a seriously out of spec yoke could also do that.