diff --git a/core/lib/Drupal/Core/Ajax/AjaxResponseAttachmentsProcessor.php b/core/lib/Drupal/Core/Ajax/AjaxResponseAttachmentsProcessor.php
index 45aa45e..4b8460c 100644
--- a/core/lib/Drupal/Core/Ajax/AjaxResponseAttachmentsProcessor.php
+++ b/core/lib/Drupal/Core/Ajax/AjaxResponseAttachmentsProcessor.php
@@ -128,7 +128,7 @@ public function processAttachments(AttachmentsInterface $response) {
    *   An array of commands ready to be returned as JSON.
    */
   protected function buildAttachmentsCommands(AjaxResponse $response, Request $request) {
-    $ajax_page_state = $request->request->get('ajax_page_state');
+    $ajax_page_state = $request->get('ajax_page_state');
 
     // Aggregate CSS/JS if necessary, but only during normal site operation.
     $optimize_css = !defined('MAINTENANCE_MODE') && $this->config->get('css.preprocess');
diff --git a/core/lib/Drupal/Core/Render/MainContent/HtmlRenderer.php b/core/lib/Drupal/Core/Render/MainContent/HtmlRenderer.php
index 54c40f6..5a2cee7 100644
--- a/core/lib/Drupal/Core/Render/MainContent/HtmlRenderer.php
+++ b/core/lib/Drupal/Core/Render/MainContent/HtmlRenderer.php
@@ -186,7 +186,7 @@ public function renderResponse(array $main_content, Request $request, RouteMatch
    * @throws \LogicException
    *   If the selected display variant does not implement PageVariantInterface.
    */
-  protected function prepare(array $main_content, Request $request, RouteMatchInterface $route_match) {
+  public function prepare(array $main_content, Request $request, RouteMatchInterface $route_match) {
     // Determine the title: use the title provided by the main content if any,
     // otherwise get it from the routing information.
     $get_title = function (array $main_content) use ($request, $route_match) {
diff --git a/core/modules/block/src/BlockRepository.php b/core/modules/block/src/BlockRepository.php
index 53620a0..eb879eb 100644
--- a/core/modules/block/src/BlockRepository.php
+++ b/core/modules/block/src/BlockRepository.php
@@ -55,6 +55,12 @@ public function getVisibleBlocksPerRegion(array &$cacheable_metadata = []) {
       /** @var \Drupal\block\BlockInterface $block */
       $access = $block->access('view', NULL, TRUE);
       $region = $block->getRegion();
+
+      // Ignore unplaced blocks.
+      if ($region == BlockInterface::BLOCK_REGION_NONE) {
+        continue;
+      }
+
       if (!isset($cacheable_metadata[$region])) {
         $cacheable_metadata[$region] = CacheableMetadata::createFromObject($access);
       }
diff --git a/core/modules/block/src/Plugin/DisplayVariant/BlockPageVariant.php b/core/modules/block/src/Plugin/DisplayVariant/BlockPageVariant.php
index 2dad5e6..35e48e5 100644
--- a/core/modules/block/src/Plugin/DisplayVariant/BlockPageVariant.php
+++ b/core/modules/block/src/Plugin/DisplayVariant/BlockPageVariant.php
@@ -135,6 +135,8 @@ public function build() {
     // Load all region content assigned via blocks.
     $cacheable_metadata_list = [];
     foreach ($this->blockRepository->getVisibleBlocksPerRegion($cacheable_metadata_list) as $region => $blocks) {
+      // Ensure there is an entry for every region.
+      $build[$region] = [];
       /** @var $blocks \Drupal\block\BlockInterface[] */
       foreach ($blocks as $key => $block) {
         $block_plugin = $block->getPlugin();
@@ -163,6 +165,12 @@ public function build() {
         // returns the blocks in sorted order.
         $build[$region]['#sorted'] = TRUE;
       }
+      // Every region for which we have cacheability metadata, must contain that
+      // cacheability metadata, otherwise the contexts by which its contents
+      // vary are impossible to know.
+      if (isset($cacheable_metadata_list[$region])) {
+        $cacheable_metadata_list[$region]->applyTo($build[$region]);
+      }
     }
 
     // If no block that shows the main content is displayed, still show the main