I suspect there are NO legal issues. Archie Comic Publications owns the work-for-hire produced for them by both Uslan and Kupperberg.
It would be somewhat more helpful to know exactly what sort of discussions or notes passed between Uslan and Kupperberg in the handoff between LWA #1 and LWA #2... but with Uslan stepping away from steering the course of the series, Kupperberg may not have felt beholden to follow ALL of Uslan's intended directions. And upon returning to the 10th Anniversary series, Uslan may have felt equally not-beholden to follow what Kupperberg established on his own after Uslan's initial departure from LWA.
It would be somewhat more helpful to know exactly what sort of discussions or notes passed between Uslan and Kupperberg in the handoff between LWA #1 and LWA #2... but with Uslan stepping away from steering the course of the series, Kupperberg may not have felt beholden to follow ALL of Uslan's intended directions. And upon returning to the 10th Anniversary series, Uslan may have felt equally not-beholden to follow what Kupperberg established on his own after Uslan's initial departure from LWA.