Check for failure of the rubber bushings in the knife drive components, there is three on each end. Also check the bearing in the one end of the connecting rod. Be sure none of the linkage or mounts is bent, cracked and broken, or distorted. Also check for movement at the clamps underneath the header which connect the three sections of the wobble hub drive shaft together. The knife is driven from the right side, the left hub is driven by a shaft running full width underneath the header. That shaft is in three pieces. Any movement on those couplers will distort timing of the two hubs. Check for possible key sheared off somewhere.
If you are out that far on register and can't adjust for it...there is something else wonky. Eliminate the simple stuff first. Possibly a shaft may be twisted. Normally the belt should slip before damage such as that occurs, but who knows