interdiff impossible; taking evasive action
reverted:
--- b/core/lib/Drupal/Core/Render/Renderer.php
+++ a/core/lib/Drupal/Core/Render/Renderer.php
@@ -209,36 +209,6 @@
       return '';
     }
 
-    // Render only the children if the internal #render_children property is
-    // set.
-    // @see \Drupal\Core\Theme\ThemeManager::render().
-    if (isset($elements['#render_children'])) {
-      // A non-empty #children property takes precedence. This happens only if
-      // it has been manually set into the render array.
-      if (!empty($elements['#children'])) {
-        $children_keys = ['#children'];
-      }
-      else {
-        $children_keys = Element::children($elements);
-
-        if (empty($children_keys)) {
-          return '';
-        }
-      }
-
-      // Remove all elements except the children because the main level has been
-      // already rendered when the #render_children is set and therefore they
-      // should not have any effect on the render children.
-      $new_elements = array_intersect_key($elements, array_flip($children_keys));
-      // Create a new variable that references the render array that was passed
-      // in. This allows the markup and cache information to be attached after
-      // rendering the new elements array.
-      $original_elements = &$elements;
-      // Change $elements to reference $new_elements. This prevents
-      // unintentional changes to the render array that was passed in.
-      $elements = &$new_elements;
-    }
-
     if (!isset($elements['#access']) && isset($elements['#access_callback'])) {
       if (is_string($elements['#access_callback']) && strpos($elements['#access_callback'], '::') === FALSE) {
         $elements['#access_callback'] = $this->controllerResolver->getControllerFromDefinition($elements['#access_callback']);
@@ -458,8 +428,10 @@
     }
 
     // Call the element's #theme function if it is set. Then any children of the
+    // element have to be rendered there. If the internal #render_children
+    // property is set, do not call the #theme function to prevent infinite
+    // recursion.
+    if ($theme_is_implemented && !isset($elements['#render_children'])) {
-    // element have to be rendered there.
-    if ($theme_is_implemented) {
       $elements['#children'] = $this->theme->render($elements['#theme'], $elements);
 
       // If ThemeManagerInterface::render() returns FALSE this means that the
@@ -468,10 +440,10 @@
       $theme_is_implemented = ($elements['#children'] !== FALSE);
     }
 
+    // If #theme is not implemented or #render_children is set and the element
+    // has an empty #children attribute, render the children now. This is the
+    // same process as Renderer::render() but is inlined for speed.
+    if ((!$theme_is_implemented || isset($elements['#render_children'])) && empty($elements['#children'])) {
-    // If #theme is not implemented and the element has an empty #children
-    // attribute, render the children now. This is the same process as
-    // Renderer::render() but is inlined for speed.
-    if (!$theme_is_implemented && empty($elements['#children'])) {
       foreach ($children as $key) {
         $elements['#children'] .= $this->doRender($elements[$key]);
       }
@@ -495,7 +467,9 @@
     // because the #type 'page' render array from drupal_prepare_page() would
     // render the $page and wrap it into the html.html.twig template without the
     // attached assets otherwise.
+    // If the internal #render_children property is set, do not call the
+    // #theme_wrappers function(s) to prevent infinite recursion.
+    if (isset($elements['#theme_wrappers']) && !isset($elements['#render_children'])) {
-    if (isset($elements['#theme_wrappers'])) {
       foreach ($elements['#theme_wrappers'] as $key => $value) {
         // If the value of a #theme_wrappers item is an array then the theme
         // hook is found in the key of the item and the value contains attribute
@@ -539,12 +513,6 @@
 
     $elements['#markup'] = Markup::create($prefix . $elements['#children'] . $suffix);
 
-    // #markup should be always saved to the referenced elements variable to
-    // prevent re-rendering.
-    if (isset($original_elements)) {
-      $original_elements['#markup'] = $elements['#markup'];
-    }
-
     // We've rendered this element (and its subtree!), now update the context.
     $context->update($elements);
 
unchanged:
--- a/core/lib/Drupal/Core/Render/Renderer.php
+++ b/core/lib/Drupal/Core/Render/Renderer.php
@@ -236,6 +236,36 @@ protected function doRender(&$elements, $is_root_call = FALSE) {
       return '';
     }
 
+    // Render only the children if the internal #render_children property is
+    // set.
+    // @see \Drupal\Core\Theme\ThemeManager::render().
+    if (isset($elements['#render_children'])) {
+      // A non-empty #children property takes precedence. This happens only if
+      // it has been manually set into the render array.
+      if (!empty($elements['#children'])) {
+        $children_keys = ['#children'];
+      }
+      else {
+        $children_keys = Element::children($elements);
+
+        if (empty($children_keys)) {
+          return '';
+        }
+      }
+
+      // Remove all elements except the children because the main level has been
+      // already rendered when the #render_children is set and therefore they
+      // should not have any effect on the render children.
+      $new_elements = array_intersect_key($elements, array_flip($children_keys));
+      // Create a new variable that references the render array that was passed
+      // in. This allows the markup and cache information to be attached after
+      // rendering the new elements array.
+      $original_elements = &$elements;
+      // Change $elements to reference $new_elements. This prevents
+      // unintentional changes to the render array that was passed in.
+      $elements = &$new_elements;
+    }
+
     $context = $this->getCurrentRenderContext();
     if (!isset($context)) {
       throw new \LogicException("Render context is empty, because render() was called outside of a renderRoot() or renderPlain() call. Use renderPlain()/renderRoot() or #lazy_builder/#pre_render instead.");
@@ -428,10 +458,8 @@ protected function doRender(&$elements, $is_root_call = FALSE) {
     }
 
     // Call the element's #theme function if it is set. Then any children of the
-    // element have to be rendered there. If the internal #render_children
-    // property is set, do not call the #theme function to prevent infinite
-    // recursion.
-    if ($theme_is_implemented && !isset($elements['#render_children'])) {
+    // element have to be rendered there.
+    if ($theme_is_implemented) {
       $elements['#children'] = $this->theme->render($elements['#theme'], $elements);
 
       // If ThemeManagerInterface::render() returns FALSE this means that the
@@ -440,13 +468,20 @@ protected function doRender(&$elements, $is_root_call = FALSE) {
       $theme_is_implemented = ($elements['#children'] !== FALSE);
     }
 
-    // If #theme is not implemented or #render_children is set and the element
-    // has an empty #children attribute, render the children now. This is the
-    // same process as Renderer::render() but is inlined for speed.
-    if ((!$theme_is_implemented || isset($elements['#render_children'])) && empty($elements['#children'])) {
+    // If #theme is not implemented and the element has an empty #children
+    // attribute, render the children now. This is the same process as
+    // Renderer::render() but is inlined for speed.
+    if (!$theme_is_implemented && empty($elements['#children'])) {
+      // Collect all bubbleable metadata from the children so that it can be
+      // applied to the mainlevel of the $elements. This way correct metadata is
+      // being applied in case $elements is being re-rendered.
+      $bubbleable_metadata = BubbleableMetadata::createFromRenderArray($elements);
       foreach ($children as $key) {
         $elements['#children'] .= $this->doRender($elements[$key]);
+        $children_bubbleable_metadata = BubbleableMetadata::createFromRenderArray($elements[$key]);
+        $bubbleable_metadata = $bubbleable_metadata->merge($children_bubbleable_metadata);
       }
+      $bubbleable_metadata->applyTo($elements);
       $elements['#children'] = Markup::create($elements['#children']);
     }
 
@@ -467,9 +502,7 @@ protected function doRender(&$elements, $is_root_call = FALSE) {
     // because the #type 'page' render array from drupal_prepare_page() would
     // render the $page and wrap it into the html.html.twig template without the
     // attached assets otherwise.
-    // If the internal #render_children property is set, do not call the
-    // #theme_wrappers function(s) to prevent infinite recursion.
-    if (isset($elements['#theme_wrappers']) && !isset($elements['#render_children'])) {
+    if (isset($elements['#theme_wrappers'])) {
       foreach ($elements['#theme_wrappers'] as $key => $value) {
         // If the value of a #theme_wrappers item is an array then the theme
         // hook is found in the key of the item and the value contains attribute
@@ -552,6 +585,17 @@ protected function doRender(&$elements, $is_root_call = FALSE) {
     $context->bubble();
 
     $elements['#printed'] = TRUE;
+
+    // #markup should be always saved to the referenced elements variable to
+    // prevent re-rendering. #cache and #attached ensures that correct cacheable
+    // metadata is applied for the re-rendered instances.
+    if (isset($original_elements)) {
+      $original_elements['#markup'] = $elements['#markup'];
+      $original_elements['#cache'] = $elements['#cache'];
+      $original_elements['#attached'] = $elements['#attached'];
+      $original_elements['#printed'] = $elements['#printed'];
+    }
+
     return $elements['#markup'];
   }
 
diff -u b/core/tests/Drupal/Tests/Core/Render/RendererTest.php b/core/tests/Drupal/Tests/Core/Render/RendererTest.php
--- b/core/tests/Drupal/Tests/Core/Render/RendererTest.php
+++ b/core/tests/Drupal/Tests/Core/Render/RendererTest.php
@@ -541,33 +541,78 @@
   }
 
   /**
-   * Tests that a first render returns the rendered output and a second doesn't.
+   * Tests rendering same render array twice.
    *
-   * (Because of the #printed property.)
+   * Tests that a first render returns the rendered output and a second doesn't
+   * because of the #printed property. Also tests that correct metadata has been
+   * set for re-rendering.
    *
    * @covers ::render
    * @covers ::doRender
+   *
+   * @dataProvider providerRenderTwice
    */
-  public function testRenderTwice() {
-    $build = [
-      '#markup' => 'test',
-    ];
-
-    $this->assertEquals('test', $this->renderer->renderRoot($build));
+  public function testRenderTwice($build) {
+    $this->assertEquals('kittens', $this->renderer->renderRoot($build));
+    $this->assertEquals('kittens', $build['#markup']);
+    $this->assertEquals(['kittens-147'], $build['#cache']['tags']);
     $this->assertTrue($build['#printed']);
 
     // We don't want to reprint already printed render arrays.
     $this->assertEquals('', $this->renderer->renderRoot($build));
+  }
+
+  /**
+   * Provides a list of render array iterations.
+   *
+   * @return array
+   */
+  public function providerRenderTwice() {
+    return [
+      [
+        [
+          '#markup' => 'kittens',
+          '#cache' => [
+            'tags' => ['kittens-147']
+          ],
+        ],
+      ],
+      [
+        [
+          'child' => [
+            '#markup' => 'kittens',
+            '#cache' => [
+              'tags' => ['kittens-147'],
+            ],
+          ],
+        ],
+      ],
+      [
+        [
+          '#render_children' => TRUE,
+          'child' => [
+            '#markup' => 'kittens',
+            '#cache' => [
+              'tags' => ['kittens-147'],
+            ],
+          ],
+        ],
+      ],
+    ];
+  }
 
+  /**
+   * Ensures that #access is taken in account when rendering #render_children.
+   */
+  public function testRenderChildrenAccess() {
     $build = [
+      '#access' => FALSE,
+      '#render_children' => TRUE,
       'child' => [
         '#markup' => 'kittens',
       ],
     ];
-    $this->assertEquals('kittens', $this->renderer->renderRoot($build));
-    $this->assertTrue($build['#printed']);
 
-    // We don't want to reprint already printed render arrays.
     $this->assertEquals('', $this->renderer->renderRoot($build));
   }