Depending on timing it may happen that the Revision GC removes a previous document without updating the main document. This can only happen in a cluster when modifications to a document happen on one cluster node and the Revision GC runs on the other cluster node. Updating the main document on Revision GC fails when the document was split after a background update that contained the latest change on the document and the document is not updated anymore. On the cluster node where the Revision GC runs, the document may then stay in the cache in a state that doesn't reflect the split. When the Revision GC runs, the main document from the cache will not show the reference to the previous document.
The Revision GC will print a log message that says like: