i ran into this issue also, the second platen is worse than the first when printing two at a time. Printing unidirectionally takes a bit longer, but seems to reduce this issue
Have you tried doing the Head Alignment.
section 6.6 of the viper manual.
Viper user guide V2.0, section 6.7 page 45
Please follow the instructions carefully, incorrect allignment procedures can result in Bi-D print looking worse. I strongly recommend that you speak with your technical representative first
Have you checked that Uni directional prints are OK?