check to make sure that the hop up unit is not binding in the mag well. The hop up units are spring loaded against the outer barrel and this effects both feeding and and air nozzle/hop up seal/compression Also....if the hop up bucking is protruding into the the hop up feed chamber you will also get poor feed/compression fps.
Remove the magwell.....push on the ho up unit toward the barrel and see if the spring action moves freely....and take it from there.
Hope this helps.....
PM me if you have any other questions