JD 337 bale length inconsistent

Set at 32-34 inch bale length for the pan style thrower. Every couple bales will be a tad shorter 26-28 inches which is no big deal. The problem is it'll make a bale that's only a third the length, like maybe four plunger strokes. Which causes the thrower not to return and gets hung up on the next bale in the chamber. Tried everything from size of windrows to baling speed and nothing seems to make a difference. Have made adjustments to the metering but nothing has helped.

Anyone know the cause of this?

JD 337 bale length inconsistent