MAGETWO-54296: Category suffix does not change after the second configuration changes

app/code/Magento/Catalog/Model/System/Config/Backend/Catalog/Url/Rewrite/Suffix.php

@@ -40,6 +40,11 @@ class Suffix extends \Magento\Framework\App\Config\Value
      */
     protected $resource;
 
+    /**
+     * @var \Magento\Framework\App\Config\ScopePool
+     */
+    private $scopePool;
+
     /**
      * @param \Magento\Framework\Model\Context $context
      * @param \Magento\Framework\Registry $registry
@@ -75,6 +80,22 @@ class Suffix extends \Magento\Framework\App\Config\Value
         $this->resource = $appResource;
     }
 
+    /**
+     * Get instance of ScopePool
+     *
+     * @return \Magento\Framework\App\Config\ScopePool
+     * @deprecated
+     */
+    private function getScopePool()
+    {
+        if ($this->scopePool === null) {
+            $this->scopePool = \Magento\Framework\App\ObjectManager::getInstance()->get(
+                \Magento\Framework\App\Config\ScopePool::class
+            );
+        }
+        return $this->scopePool;
+    }
+
     /**
      * Check url rewrite suffix - whether we can support it
      *
@@ -103,6 +124,24 @@ class Suffix extends \Magento\Framework\App\Config\Value
         return parent::afterSave();
     }
 
+    /**
+     * @return $this
+     */
+    public function afterDeleteCommit()
+    {
+        if ($this->isValueChanged()) {
+            $this->updateSuffixForUrlRewrites();
+            if ($this->isCategorySuffixChanged()) {
+                $this->cacheTypeList->invalidate([
+                    \Magento\Framework\App\Cache\Type\Block::TYPE_IDENTIFIER,
+                    \Magento\Framework\App\Cache\Type\Collection::TYPE_IDENTIFIER
+                ]);
+            }
+        }
+
+        return parent::afterDeleteCommit();
+    }
+
     /**
      * Check is category suffix changed
      *
@@ -135,7 +174,12 @@ class Suffix extends \Magento\Framework\App\Config\Value
         }
         $entities = $this->urlFinder->findAllByData($dataFilter);
         $oldSuffixPattern = '~' . preg_quote($this->getOldValue()) . '$~';
-        $suffix = $this->getValue();
+        if ($this->getValue() !== null) {
+            $suffix = $this->getValue();
+        } else {
+            $this->getScopePool()->clean();
+            $suffix = $this->_config->getValue($this->getPath());
+        }
         foreach ($entities as $urlRewrite) {
             $bind = $urlRewrite->getIsAutogenerated()
                 ? [UrlRewrite::REQUEST_PATH => preg_replace($oldSuffixPattern, $suffix, $urlRewrite->getRequestPath())]