OK, one more possibility. As the bolt is pulled back, the extractor forces the case to the left, where it drags against the receiver wall. (This friction is what normally ejects the empty case - long before the rim could strike the ejector.) If the extractor spring is strong and the wall is rough and/or dry, the resultant friction can retard bolt movement significantly.
https://www.milsurps.com/images/impo.../leeextr-1.jpg
Try smearing a little good grease on the wall where the cartridge rim drags. If that makes things better, polishing the site of the friction may help, as may keeping it lubed.