Resolve "404 seems to be broken again"

Closes #844 (closed)

aleksis/core/frontend/components/app/App.vue

@@ -86,7 +86,7 @@
           </div>
 
           <error-page
-            v-if="error404 && !$root.contentLoading"
+            v-if="error404"
             short-error-message-key="network_errors.error_404"
             long-error-message-key="network_errors.page_not_found"
             redirect-button-text-key="network_errors.back_to_start"
@@ -230,6 +230,7 @@ import useRegisterSWMixin from "../../mixins/useRegisterSW";
 import offlineMixin from "../../mixins/offline";
 import menusMixin from "../../mixins/menus";
 import routesMixin from "../../mixins/routes";
+import error404Mixin from "../../mixins/error404";
 
 export default {
   data() {
@@ -281,16 +282,6 @@ export default {
       },
       deep: true,
     },
-    $route: {
-      handler(newRoute) {
-        if (newRoute.matched.length === 0) {
-          this.error404 = true;
-        } else {
-          this.error404 = false;
-        }
-      },
-      immediate: true,
-    },
   },
   name: "App",
   components: {
@@ -302,7 +293,7 @@ export default {
     SideNav,
     SnackbarItem,
   },
-  mixins: [useRegisterSWMixin, offlineMixin, menusMixin, routesMixin],
+  mixins: [useRegisterSWMixin, offlineMixin, menusMixin, routesMixin, error404Mixin],
 };
 </script>