only in patch2:
unchanged:
--- a/core/lib/Drupal/Core/Flood/MemoryBackend.php
+++ b/core/lib/Drupal/Core/Flood/MemoryBackend.php
@@ -41,7 +41,7 @@ public function register($name, $window = 3600, $identifier = NULL) {
     // We can't use REQUEST_TIME here, because that would not guarantee
     // uniqueness.
     $time = microtime(TRUE);
-    $this->events[$name][$identifier][$time + $window] = $time;
+    $this->events[$name][$identifier][strval($time + $window)] = $time;
   }
 
   /**