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This error is caused by the discontinued Atlassian's plugin Subversion for Jira. It has a bug and the service is not removed along with the app and it remains active causing errors. It must be manually removed from the Jira administration services section and reboot Jira.

Cannot authenticate

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in a repository 

Try by configuring the order to negotiate authentication by adding the following property to the JVM configuration and re-starting Jira:

-Dsvnkit.http.methods=Basic,Digest,Negotiate,NTLM