Use active file instead.

app/assets/javascripts/repo/components/repo_editor.vue

@@ -17,7 +17,7 @@ const RepoEditor = {
     Service.getRaw(this.activeFile.raw_path)
     .then((rawResponse) => {
       Store.blobRaw = rawResponse.data;
-      Helper.findOpenedFileFromActive().plain = rawResponse.data;
+      Store.activeFile.plain = rawResponse.data;
 
       const monacoInstance = this.monaco.editor.create(this.$el, {
         model: null,