Whereas a Case is a specific report from a customer, Issues correspond to general problems that can be encountered by an a customer. Therefore, there can be many cases reported for the same issue. Likewise, a single case report could reference multiple issues.
Aptify tracks the relationship between cases and issues on the Related Issues tab of a Cases record. See About the Cases Form for more details details.
Issue
Specifies an issue that applies to this case. This field links to the Issues service.