In so much as that if the user can’t access the category then they won’t be able to select it when creating a topic (and if they can’t choose it when creating a topic then your ‘allowed tag’ structure also won’t kick in). Is the user a part of a group who can access those categories?
I think if you’ve not landed on what the conflict is yet you may need to start removing some of the tag restrictions and see if you can narrow down exactly where the permission conflict is happening.