Steps to reproduce the issue

I have created an override of an article view to restructure the content.
I have separated intro and full text and positioned the article image in between.

<?php echo $this->item->introtext; ?>
....
<?php echo LayoutHelper::render('joomla.content.full_image', $this->item); ?>
...
<?php echo $this->item->fulltext; ?>

As a result, the plugin for inserting the custom fields is no longer executed.
The reason for this is that it only reacts to intro ($item->introtext;) and entire text ($item->text)
Adding a function for $item->fulltext helps

Solution

 // Prepare the fulltext
              if (property_exists($item, 'text') && strpos($item->fulltext, 'field') !== false) {
            $item->fulltext = $this->prepare($item->fulltext, $context, $item);
        }