I have 2 8820s , one with a JD feeder house chain  other one with a  Harvest Sevice  feeder house chain  . We put new chains and sprockets  and reused the slats on the Harvest service chain and cut  600 acres of wheat  with no problems changed to corn and had exact same problem as you only on  the left side . We did about everthing even put the steel JD slats back in  never helped .  Finally we  took the chain back out and swapped the side chains right to left and  putt he Harvest service slats back in ,I like them better in   wheat . Cut 600 acres of wheat this year without  a issue . I think it was a cob  issue .  I got real good at getting the chain back in time ,we  even tired the other 8820 with the JD chain and had no problems  .  A 8820 has 4 chains  we always had our problem with  the outer  chain under the cab.