Till the Blood Runs Clear - S1-E11
Continuity mistake: When Rorf and Rorg are firing at John and D'Argo who are pinned down in an area with no "back door," the lens surface on John's goggles are scratched/cracked, but once John makes the comment about soldiers of fortune and Aeryn walks out, the small holes on both lenses are now perfectly intact.
Chosen answer: It's never explained. John mentions a theory that his less technologically developed craft simply interferes with the wormhole less than the "superior" Vipers, but they never make a concrete determination on that point. But we also have to take into account the fact that Moya traverses wormholes with no ill effect as well.
Garlonuss ★