Each JIRA issue only supports up to 13 records of Salesforce Objects.
If you are trying to associate more than 13 records through the Manage Application Link or Associate endpoints the Connector will prevent you from making more.
For Connector Versions 5.4 and Later
Starting from version 5.4 of the Connector, JIRA Issues being limited to 13 Salesforce Objects has been resolved. This update removes this limit, allowing users to associate as many remote objects as they want in an issue.
However, once upgraded, you are not advised to downgrade to earlier versions. If you do downgrade, due to the way the data is stored, the data related to the association of the issue and the remote objects may no longer be viewable.