Thank you for contacting WPML support. While you are waiting for one of my colleagues to take this ticket and work on it, let me provide you with the first debugging steps and try to help with the issue quickly.
Thank you. We did end up removing products and reimporting them with proper language priority set this time, but had this been a properly populated site it could have been different. Would be awesome if there was a way to "bulk" switch default language for products, but after digging into it a bit more I understand that this includes connected elements, taxonomies, etc.