--- services/project-history/app/js/UpdateTranslator.js
+++ services/project-history/app/js/UpdateTranslator.js
@@ -73,9 +73,18 @@ function _convertToChange(projectId, updateWithBlob) {
     throw error
   }

+  let v2Authors
+  if (update.meta.user_id === 'anonymous-user') {
+    // history-v1 uses null to represent an anonymous author
+    v2Authors = [null]
+  } else {
+    // user_id is missing on resync operations that update the contents of a doc
+    v2Authors = _.compact([update.meta.user_id])
+  }
+
   const rawChange = {
     operations,
-    v2Authors: _.compact([update.meta.user_id]),
+    v2Authors,
     timestamp: new Date(update.meta.ts).toISOString(),
     projectVersion,
     v2DocVersions: Object.keys(v2DocVersions).length ? v2DocVersions : null,