Any burs on the ejector rod? Is it smooth? Any build up inside the frame, try removing the side plate an checking for any debris? If shooting lead bullets you can get a build up in the forcing cone that would cause it to stick
Dam if your weren’t that far I’d help you. I’ve been building these guns for over 30 years and work for a AR manufacturer. Sounds like you have hammer follow which could be as simple as the hammer spring was installed wrong, or the hammer and trigger have been “bubbafide” so they won’t hold on...