Good points. I use mostly steel hulled gun club hulls for my reloads. I clean my guns quite well as with little oil since that is like a magnet for burnt powder. I wondered about the two springs on each side of chamber but they should not interfere with extraction...I think.Multiple quick things to check. Is it with all brands of ammo or one type? The extractor could be dirty, chamber could be dirty.
Are you dropping the shell into the chamber then closing the action or dropping the shell in and letting the lifter bring the shell up into the chamber?
You might not be getting the action closed hard enough for the extractor to close around the rim of the shell.
Pull the barrel and make sure the grove where the extractor sits when the action is closed is good a clean and the area behind the edge of the extractor is clean.