I have a list of subscriptions to add to Membership Pro and that part works great. I'm familiar with the CSV and use MS Access to generate the file I need. I though that when importing a subscription the subscriber would also be added to the selected MailChimp audiences. If I add a new subscriber then they are added to MailChimp correctly so the interface is working correctly.
When I first set up the web site a couple of years ago I imported all the subscribers and they were added to MailChimp. I don't remember doing a separate import into MailChimp.
I tested this again with clean data and it works as expected. I end up with a subscription in Membership Pro and an entry in MailChimp.
My original issue may have been bad data or MailChimp may no allow gmail "+" aliases any more. Most of our test data used this gmail feature to test many subscribers without needing to create temporary email accounts.