Just a thought--if you changed/created the join in Tableau instead of within Access itself would that bring the data in correctly?
That is something I would like to try next, as a temporary workaround I am running a make table query in Access, then connecting to that table. The query contains many tables and complex joins, therefore it will take a bit of work to recreate through Tableau. I have heard from several people though that creating the joins in Tableau is the way to go! Thank you for your suggestion.