When you have a course with multiple instances of the self enroll plug-in added to it, the students are seeing multiple instances of "Enrollment is disabled or inactive" when trying to enroll in the course and guest see multiple instances of "Guests can not access this course, please try to log in."

This was not the case in 2.6 - but seems to be new behavior in 2.7 and 2.8.

To replicate:
Create a test course and add a self enrollment instance to the course with a start date of May 1 2015 and an end date of May 7, 2015, name it test1 and save.
Add another self enrollment instance with dates of May 8, 2015 to May 15, 2015, name it test 2 and save.
Now try to access the course as a guest or as an authenticated user on the site. You will see two messages in regards to the enrollment not being available.
In 2.6 you did not get this result.