Users are not being enrolled down into child courses.
Are all child courses published?
Are all child courses set as ‘public’ for privacy settings? (EthosCE 7.4+)
Are all child courses open for enrollment (not closed/expired)?
Do the child courses have enrollment prerequisites?
When viewing the error log under the Admin wrench -> Administration -> Recent log -> Filter by Type:cron messages, is cron completing successfully?
Were the child courses added after users had enrolled?
Are there any role restrictions set on the parent or child courses?