When performing an import the JIRA instance hangs and the logs show the following error message:
The XML export was generated from an instance with some specific third party plugins installed on it.
Behaviour and Workaround explained at Could not find entity for entityName - when restoring a XML backup into a JIRA application
The JIRA instance shouldn't hang. On OnDemand users are not able to login and see a 500 error message screen until it is manually restarted. No error message is displayed explaining the error.