Before v5.1.0, Checklist’s CSV export would split each item into three columns:
Checklist Item Name ([custom field name])
Checklist Item Completed ([custom field name])
Checklist Item Status ([custom field name])
Why the change?
The biggest reason is that the new export format is now compatible with how Jira imports CSV. Also, the new format is more flexible and allows you to add any metadata fields, such as the assignee and due date, and facilitates future improvements to the structure.