If the follower can be pushed down easily enough but it stops hard at four rounds then there may be a burr inside the mag that is causing the follower to stick when it is held in the right position for loading ammo. Pull it apart and check.
So I fixed it with the dremel..I trimmed a bit of material off the follower where it was getting hung up.. Works like a charm now. Both magazines that came with the gun were doing it..



























