Learners Incorrectly Receiving 'Can't Enroll Now' error on Required Courses

Learners assigned to required courses are receiving the below message on their assigned learning;

"Can't Enroll Now - You can't create this assignment because the learner already has an existing assignment for this learning item."

However, there is no existing assignment.
In the admin assignment page, there is 1 active assignment with the status 'No Active Offering' .

This is happening on multiple courses for multiple learners.

Has anyone else experienced this issue and can suggest how to resolve this?

Thanks

Megan