I’m sorry that you’re going through this as well. I’m a week behind you here and I have tried everything I know how to do. Did you ever find a solution?
When I go to tag products, only one of my items pops up and is available for tagging. If I do use that tag, it can still link back to my Instagram/Facebook shop where I can see all of my products so I don’t understand why only one showing up whenever I try to tag product in an Instagram post.