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Have you tried to remove JSU app and reinstall it in the JIRA administration? (Without restarting JIRA)
See also https://confluence.atlassian.com/upm/uninstalling-appsadd-ons-273875709.html .
If re-installation of the app in the JIRA administration does not work, try to do it with a restart of JIRA, follow this steps:
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