You probably need to contact Atlassian's OnDemand support to get this one fixed - it needs people to look at configuration and possibly logs, and we're just end-users, we have no access to your OnDemand instance.
Checking by the error message is possible that your group name is not being recognized. Could you take a look at the following links and check if it helps?
Two vulnerabilities have been published for Confluence Server and Data Center recently: March 20, 2019 CVE-2019-3395 / CVE-2019-3396 April 17, 2019 CVE-2019-3398 The goal of this article is...
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