Confluence Sidebar is blank and Space Tools is missing on some instances

Summary

When you access a Space, the sidebar is blank and Space Tools is missing.

This message is seen in the logs

2017-02-01 11:31:42,989 ERROR [ajp-nio-8009-exec-121] [plugin.descriptor.web.ConfluenceWebInterfaceManager] getHtml Failed to render web panel: com.atlassian.plugin.web.descriptors.DefaultWebPanelModuleDescriptor$ContextAwareWebPanel@40857e64
 -- url: /display/KEY/Page | page: 4260294 | traceId: 5589811101dedf7a | userName: username | referer: https://confluence.company.com/spacedirectory/view.action | action: viewpage
java.lang.RuntimeException: Entities can only be used with a single EntityManager instance

Environment

Confluence 1000.27.0

Steps to Reproduce

1. Be on a instance with duplicate entry in AO_187CCC_SIDEBAR_LINK table (unknown how to reproduce this step)
2. Access a Space
3. The sidebar is showing blank and Space Tools is missing

Expected Results

• Confluence Sidebar and Space Tools should be visible

Actual Results

• Confluence Sidebar is blank and Space Tools is missing

Resolution

1. Verify if there is a Duplicate Entry in "AO_187CCC_SIDEBAR_LINK"

   select * from "AO_187CCC_SIDEBAR_LINK" where "CATEGORY" = 'ADVANCED' AND "SPACE_KEY"='{SPACEKEY}';

   select * from "AO_187CCC_SIDEBAR_LINK" where "CATEGORY" = 'MAIN' AND "SPACE_KEY"='{SPACEKEY}';

2. Once duplicate entry is identified, delete the duplicate entry by running the command:

   delete from "AO_187CCC_SIDEBAR_LINK" where "ID" = {ID of the duplicate entry};

3. Flush cache

Note: Don't forget to backup the database