I only own one of these, so I can only suggest where I would check if I had the problem. Look to be sure the barrel is timed on the receiver correctly so the op-rod is coming straight back and is not shoving the roller at an angle. Check that the op-rod guide isn't worn excessively. If you can, swap in the gas system from another gun to try it. That might help isolate the problem. Kuhnhausen has pretty good detail on op-rod fit, and you might check there for tips.
Walt Kuleck sometimes posts on this forum and he may well have other suggestions.