Relation with issues
Since CRM version 4.3.0 issue-contact and issue-deal relation model moved to Custom fields
Contact can be associated with issues, deals, invoices, expenses, operations and products. All of them will be shown in contact's profile. User might associate all these items from their pages or directly from contact page (using right sidebar or main bar under contact's name).
To add relation between Contact and Issue just create new Issue Custom Field of Contact type.
You can also show closed issues on contact's view. In order to enable it, go to Administration -> Contacts. There will be a field called Show closed issues - you should check it in.
Extract old version existed relation
bundle exec rake redmine:contacts:convert_links_to_custom_fields RAILS_ENV=production