We are going through the same problem.
After upgrading to the latest versions of WordPress, WooCommerce and Moodle, we noticed in our tests that new users are not being enrolled in Moodle after purchasing a course in the store. Now, when I buy a course with a user who has already purchased a course, it is usually directed to Moodle.
Could you help us?
Wordpress: 5.0.3
WooCommerce: 3.5.4
MooWoodle: 1.3.0
Moodle 3.5.2+ (Build: 20181107)