This is a problem with the applinks configuration on your Confluence instance. For OnDemand, you will need to submit a support request and ask a support engineer to look into the problem.
Usually a support engineer can solve this by simply deleting Confluence's JIRA applink and restarting Confluence, so you will need to let them know an appropriate time they can restart Confluence (meaning the wiki will be inaccessible for ~10 minutes).
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