Issue #2870661 by Peacog: Grouped filter with custom identifier not added to secondary options

src/Plugin/views/exposed_form/BetterExposedFilters.php

@@ -1137,7 +1137,14 @@ Off|No
 
       // Check if this is a secondary form element.
       if ($allow_secondary && $settings[$label]['more_options']['is_secondary']) {
-        $identifier = $form['#info']["filter-$label"]['value'];
+        if ($filters[$label]->options['is_grouped']) {
+          $identifier = $filters[$label]->options['group_info']['identifier'];
+          $filter_info_name = "filter-$identifier";
+        }
+        else {
+          $identifier = $filters[$label]->options['expose']['identifier'];
+          $filter_info_name = "filter-$label";
+        }
         if (!empty($form[$identifier])) {
           // Move exposed operators with exposed filters
           if (!empty($this->display->display_options['filters'][$identifier]['expose']['use_operator'])) {
@@ -1147,8 +1154,8 @@ Off|No
           }
           $secondary[$identifier] = $form[$identifier];
           unset($form[$identifier]);
-          $secondary[$identifier]['#title'] = $form['#info']["filter-$label"]['label'];
-          unset($form['#info']["filter-$label"]);
+          $secondary[$identifier]['#title'] = $form['#info'][$filter_info_name]['label'];
+          unset($form['#info'][$filter_info_name]);
         }
       }
     }