Steps to Reproduce:

1. Install a fresh Confluence 5.10.7
2. Restore a Cloud Backup
3. Create / Edit pages

Actual behavior:

Page spinning forever and following error appears in logs:

2016-10-13 09:36:57,463 ERROR [http-nio-8090-exec-10] [confluence.plugins.synchrony.SynchronyContextProvider] getContextMap This instance could not be registered with Synchrony.
 -- space: 1638403 | url: /plugins/editor-loader/editor.action | page: 26705975 | traceId: 0d013bf225cda166 | userName: sysadmin | referer: http://localhost:8090/pages/viewpage.action?pageId=26705975 | action: editor

Expected Behavior:

Since you can restore cloud backup into 5.10 and later (here) you should be able to edit and create pages

Workaround for Confluence 5.10):

1. Navigate to <base URL>/admin/darkfeatures.action
2. Remove:
   1. site-wide.synchrony
   2. site-wide.synchrony.opt-in
   3. site-wide.shared-drafts

Workaround for Confluence 6.0+:

This issue does not affect customers on Confluence 6.0 or greater. If you are experiencing issues editing pages after upgrade, please see Troubleshooting Collaborative Editing