Issue #3472326 Unable to remove item at non-existing index.

Related to #3472326

src/Plugin/Field/FieldFormatter/EntityReferenceExportFormatter.php

@@ -31,11 +31,19 @@ class EntityReferenceExportFormatter extends EntityReferenceEntityFormatter {
   public function view(FieldItemListInterface $items, $langcode = NULL): array {
     $elements = $this->viewElements($items, $langcode);
 
+    $deltasToRemove = [];
     foreach ($items as $k => $item) {
-      if (empty($elements[$k]) && $item->entity) {
-        $items->removeItem($k);
+      if (!empty($elements) && !isset($elements[$k]) && $item->entity) {
+        $deltasToRemove[] = $k;
       }
     }
+    // Field item deltas are reset when an item is removed. This removes
+    // items in descending order so that the deltas yet to be removed will
+    // continue to exist and can be removed in a future loop.
+    rsort($deltasToRemove);
+    foreach ($deltasToRemove as $delta) {
+      $items->removeItem($delta);
+    }
 
     $elements = array_values($elements);
     $output = ['#items' => $items];