AppID's that contain special characters are rejected by Synchrony.

2016-08-17 15:27:42,711 WARN [synchrony-interop-executor:thread-1] [plugins.synchrony.config.DefaultSynchronyConfigurationManager] logJSONResponseField [Collab editing plugin] Response message for Schäferbarthold-GmbH-389d808a-b63c-3389-93c3-26ff2b9ab16d: Invalid AppID format

Workaround

1. We generate the AppID using the organisation name from the license. Since this is EAP if it is possible to obtain an evaluation license under a org name that does not contain special characters then that should mitigate this issue.
2. If you upgraded Confluence from a milestone version and saw this problem, please try to turn Synchrony OFF and ON in the Collaborative Editing administration page (so that a new App ID will be generated). Please note that a Synchrony restart won't help.