i would look at the trigger and A/T cam to start, then look at the lug last.
hold the gun in your right hand and tilt to the left, while looking at the A/T cam. If the A/T cam slide out a bit, it could be the cam and trigger binding. I have had this problem before and it can also make it feel like you're pinching balls as to push the pump handle foward. if this is the case tighten the small screw that under the trigger. (i forgot the name) you'll notice once it's too tight cause the pump stroke will bind so back it up if you go too far. you have to find the medium where it doesn't bind the pump stroke and it's not loose where the cam will slide to the left to also bind.
another is a worn out trigger. a team mate had this issue. were the cam rests on the trigger it had worn out a groove but it had like frayed delrin on the edge. you know when you cut plastic and the edge builds up. and that was getting caught on the edge of the cam where the flat and round part meet. causing it to bind.
last your lug can be loose? but it seems like one of the above.