If you are on Cloud and you're still running into this issue try the JIRA App from the App store and see if you're able to login. If this is server, does this work in another browser,e.g. Chrome, Firefox?
I would also check to make sure the JIRA Mobile module is enabled:
Hi team, I’m Avinoam, a product manager on Confluence Cloud, and today I’m really excited to let the Community know that all customers can now try out the new editing experience and see some of the ...
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