Heavy ink films/densities in prior units are increasing the opportunity for poor trapping.
Lower densities of prior colors and increase density of latter units or change rotation. Lower the tack of the ink, if necessary, with 2-5% gelled reducer.
Paper may have high hold out (low absorption).
This prevents the inks from setting into the paper and tacking up between units, leading to poor trapping and tacking up between units.
Blankets are not releasing ink well.
Check blanket compatibility with ink system. Change blanket.