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There are some scenarios that could cause your user to don't be able to login after a system restore from an XML backup in Jira. Without further investigate the logs, I suggest you check the following KBs:
In order to better diagnose and compare your current scenario with the one you are facing right now, we suggest you check the error in your Atlassian-jira.logs file when you try to log in.
Let us know if you have any questions. In case the KBs above did not help, please provide us with the logs you find in Atlassian.logs
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