Patch form of change from MR https://www.drupal.org/project/drupal/issues/2821962#comment-15758857 (comment #81). Also, rerolled to make it apply as we already have patch https://www.drupal.org/project/drupal/issues/2787051#comment-14166134 which preent directly applying of this patch.

2821962-81.patch

diff --git a/core/modules/views/src/Form/ViewsExposedForm.php b/core/modules/views/src/Form/ViewsExposedForm.php
index d68b1dd5363..828ca44ea9c 100644
--- a/core/modules/views/src/Form/ViewsExposedForm.php
+++ b/core/modules/views/src/Form/ViewsExposedForm.php
@@ -10,6 +10,7 @@
 use Drupal\Core\Render\Element\Checkboxes;
 use Drupal\Core\Url;
 use Drupal\views\ExposedFormCache;
+use Drupal\views\Views;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 
 /**
@@ -53,7 +54,7 @@ public function __construct(ExposedFormCache $exposed_form_cache, CurrentPathSta
   public static function create(ContainerInterface $container) {
     return new static(
       $container->get('views.exposed_form_cache'),
-      $container->get('path.current')
+      $container->get('path.current'),
     );
   }
 
@@ -74,6 +75,13 @@ public function buildForm(array $form, FormStateInterface $form_state) {
     /** @var \Drupal\views\ViewExecutable $view */
     $view = $form_state->get('view');
     $display = &$form_state->get('display');
+    // Existing arguments need to be passed as this exposed form might
+    // be used in a block. Without this contextual views arguments
+    // will be lost.
+    if ($this->getRouteMatch()->getRouteObject() && $this->getRouteMatch()->getRouteName() !== 'views.ajax' && empty($view->args)) {
+      $args = Views::buildArgs($this->getRouteMatch());
+      $view->setArguments($args);
+    }
 
     $form_state->setUserInput($view->getExposedInput());
 
@@ -132,7 +140,15 @@ public function buildForm(array $form, FormStateInterface $form_state) {
       }
     }
     else {
-      $form_action = $view->getUrl()->toString();
+      $view_url = $view->getUrl();
+      $parameters = [];
+      foreach ($view_url->getRouteParameters() as $k => $parameter) {
+        $parameters[$k] = $parameter;
+      }
+      if (!empty($parameters)) {
+        $view_url->setRouteParameters($parameters);
+      }
+      $form_action = $view_url->toString();
     }
 
     $form['#action'] = $form_action;
diff --git a/core/modules/views/src/Routing/ViewPageController.php b/core/modules/views/src/Routing/ViewPageController.php
index 665e5bd31a8..68a46719f9b 100644
--- a/core/modules/views/src/Routing/ViewPageController.php
+++ b/core/modules/views/src/Routing/ViewPageController.php
@@ -98,28 +98,8 @@ public function title($view_id, $display_id, RouteMatchInterface $route_match) {
    *   The route arguments.
    */
   protected function getRouteArguments(RouteMatchInterface $route_match) {
-    $args = [];
+    $args = Views::buildArgs($route_match);
     $route = $route_match->getRouteObject();
-    $map = $route->hasOption('_view_argument_map') ? $route->getOption('_view_argument_map') : [];
-
-    foreach ($map as $attribute => $parameter_name) {
-      // Allow parameters be pulled from the request.
-      // The map stores the actual name of the parameter in the request. Views
-      // which override existing controller, use for example 'node' instead of
-      // arg_nid as name.
-      if (isset($map[$attribute])) {
-        $attribute = $map[$attribute];
-      }
-      if ($arg = $route_match->getRawParameter($attribute)) {
-      }
-      else {
-        $arg = $route_match->getParameter($attribute);
-      }
-
-      if (isset($arg)) {
-        $args[] = $arg;
-      }
-    }
     return $args;
   }
 
diff --git a/core/modules/views/src/Views.php b/core/modules/views/src/Views.php
index 1d443d4093d..0171f6faf8f 100644
--- a/core/modules/views/src/Views.php
+++ b/core/modules/views/src/Views.php
@@ -2,6 +2,8 @@
 
 namespace Drupal\views;
 
+use Drupal\Core\Routing\RouteMatchInterface;
+
 /**
  * Static service container wrapper for views.
  */
@@ -537,4 +539,40 @@ protected static function t($string, array $args = [], array $options = []) {
     return static::$translationManager->translate($string, $args, $options);
   }
 
+  /**
+   * Builds args.
+   *
+   * @param \Drupal\Core\Routing\RouteMatchInterface $route_match
+   *   The route match.
+   *
+   * @return array
+   *   Array of args.
+   */
+  public static function buildArgs(RouteMatchInterface $route_match): array {
+    $args = [];
+    $route = $route_match->getRouteObject();
+    $map = $route->hasOption('_view_argument_map') ? $route->getOption('_view_argument_map') : [];
+
+    foreach ($map as $attribute => $parameter_name) {
+      // Allow parameters be pulled from the request.
+      // The map stores the actual name of the parameter in the request. Views
+      // which override existing controller, use for example 'node' instead of
+      // arg_nid as name.
+      if (isset($map[$attribute])) {
+        $attribute = $map[$attribute];
+      }
+
+      $arg = $route_match->getRawParameter($attribute);
+      if (!$arg) {
+        $arg = $route_match->getParameter($attribute);
+      }
+
+      if (isset($arg)) {
+        $args[] = $arg;
+      }
+    }
+
+    return $args;
+  }
+
 }