Users need to reconsent the app
The architecture of the Cloud app is different from the Data Center app. Therefore if users have already consented the SharePoint Connector for Jira in Data Center they would need to reconsent it in order to continue using it in cloud.
SharePoint web part integration
All web parts created prior to the migration which were connecting Jira Data Center to SharePoint Online will stop working after the migration.
Web parts need to be recreated manually after connecting to the new Cloud instance.