It's not clear how workers would have received the impression that there was a policy change. Amazon's ad policies bar ads that "advocates or demeans" a religion, but that doesn't preclude selling religious material in the first place.

Whatever the explanation, the takedowns have apparently done significant damage to sales for at least some sellers. And that's a significant problem when ads are vital on Amazon's store -- they're the best chance at visibility for a product outside of Amazon's own recommendations. Whole companies are highly dependent on Amazon's ad system for success, and even a seeming slip-up can have dramatic consequences.