Sorry, sir for the delay in reply.
I checked this issue at my local setup and your live setup too.
There is some bug from our side.
Thanks for credentials and acknowledgment.
I am adding your issue to trello. Hopefully, it's solution will release in the next update.
Well, we can't say about timing. But If You are in a hurry then we can make this in the priority list and try to deliver its solution as soon as possible. I personally ask our developer team to provide a solution in this query.
You said when you click on sync all users, nothing changed on MailChimp.
These are the data I am seeing: http://prntscr.com/op2i0b
You can see there are data, that means sync is working. If you want to check live please make an activity then check.
I created a new course test course and purchased that course so according to settings, If we click on sync all users (Enable Subscribe option in WooCommerce Checkout) It should be added in MailChimp List( Woocomerce opcion de suscripción).
I clicked and you can see new entries in Woocomerce opcion de suscripción list.
Please check at your end and reply. Now it should work.
I am really thankful for your time.