“The Russians believe that continued operations are safe but they can’t prove to our satisfaction that they are, and the U.S. believes that it’s not safe but we can’t prove to the Russians’ satisfaction that that’s the case,” he added.

Russian teams believe the air leak was likely caused by high cyclic fatigue from micro vibrations, while teams at NASA think pressure and mechanical stress, residual stress, material properties of the module, and environmental exposure are all at play, according to SpaceNews.