.../src/EventSubscriber/SmartCacheSubscriber.php         | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/core/modules/smart_cache/src/EventSubscriber/SmartCacheSubscriber.php b/core/modules/smart_cache/src/EventSubscriber/SmartCacheSubscriber.php
index 2639134..384d889 100644
--- a/core/modules/smart_cache/src/EventSubscriber/SmartCacheSubscriber.php
+++ b/core/modules/smart_cache/src/EventSubscriber/SmartCacheSubscriber.php
@@ -140,13 +140,14 @@ public function onRouteMatch(GetResponseEvent $event) {
 
     // Get the contexts by which the current route's response must be varied.
     $cid = implode(':', $this->cacheContextsManager->convertTokensToKeys(['route'])->getKeys());
-    $cache_contexts_for_route = $this->smartContextsCache->get($cid);
+    $cached = $this->smartContextsCache->get($cid);
+    $cache_contexts_for_route = ($cached !== FALSE) ? $cached->data : NULL;
     $request->attributes->set(self::ATTRIBUTE_CACHE_CONTEXTS_FOR_ROUTE_CID, $cid);
     $request->attributes->set(self::ATTRIBUTE_CACHE_CONTEXTS_FOR_ROUTE, $cache_contexts_for_route);
 
     // Get & set the cached HTML response for the current route, if any.
-    if ($cache_contexts_for_route !== FALSE) {
-      $cid = implode(':', $this->cacheContextsManager->convertTokensToKeys($cache_contexts_for_route->data)->getKeys());
+    if (is_array($cache_contexts_for_route)) {
+      $cid = implode(':', $this->cacheContextsManager->convertTokensToKeys($cache_contexts_for_route)->getKeys());
       $cached_html = $this->smartHtmlCache->get($cid);
       if ($cached_html !== FALSE) {
         $response = $cached_html->data;
@@ -218,8 +219,7 @@ public function onResponse(FilterResponseEvent $event) {
       $this->normalizeCacheability($html_cacheability);
 
       // Get the contexts by which the current route's response must be varied.
-      $cache_contexts_for_route = $request->attributes->get(self::ATTRIBUTE_CACHE_CONTEXTS_FOR_ROUTE);
-      $stored_cache_contexts = ($cache_contexts_for_route !== FALSE) ? $cache_contexts_for_route->data : NULL;
+      $stored_cache_contexts = $request->attributes->get(self::ATTRIBUTE_CACHE_CONTEXTS_FOR_ROUTE);
 
       // If the set of cache contexts is different, store the union of the
       // already stored cache contexts and the contexts for this request.
@@ -265,6 +265,12 @@ protected function normalizeCacheability(CacheableMetadata $cacheability) {
    */
   public static function getSubscribedEvents() {
     $events = [];
+
+    // Run after AuthenticationSubscriber (necessary for the 'user' cache
+    // context) and MaintenanceModeSubscriber (SmartCache should not be polluted
+    // by maintenance mode-specific behavior), but before
+    // ContentControllerSubscriber (updates _controller, but that's pointless
+    // when SmartCache runs).
     $events[KernelEvents::REQUEST][] = ['onRouteMatch', 27];
 
     // Run before HtmlResponseSubscriber::onRespond(), which has priority 0.