We are getting the following error message when we attempt to create an epic, "Unfortunately, there is an internal communication error, so you must use the full dialog to create the issue. Please contact your administrator if this error keeps appearing." We have no issue creating a user story or bug in the same project. So the issue is only appearing when attempting to create the epic.
You will have to go to the Jira logs at $JIRA-Home/log and tail the atlassian-jira.log. Then reproduce the issue and check what error shows up on the logs when you try to create an Epic. There should probably be an existing KB highlighting the error and the resolution once you find the stack trace.
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