The problem is the cam assembly. The agitator dogs are worn out.
It's a simple repair. (If over five years old...recommend replacing the cam assembly, inner cap/o-ring and thrust spacer.
Pull out the softener basket. Reach in and grasp the tabs on the inner cap and pull. Remove the center bolt (ratchet, six inch extension and socket). Remove the entire agitation assembly. Hold the lower while giving a good tug to separate the upper. Replace the thrust spacer on the lower agitator. Place the upper back on and pop in the cam assembly. Place agitation assembly back in washer. Place center bolt in and snug it up hand tight. Place inner cap (thin layer of liquid detergent on o-ring makes it easy) and then replace the softener dispenser. Done!