Disappearing Background Images

I have the same problem, @frazras did you solved this?

The problem, as @frazras comments, is that the function submitConfigurationForm never triggers but neither of this plugin nor of others of the style options.

Finally I have done it in a not very optimal way, but the only one I have seen.

From a hook_node_update I go through all the paragraphs looking for the style options that has the backgroun image and I do the same thing that should be done in the submitConfigurationForm.

This is my code in case someone wants to use it or improve it:

use Drupal\Core\Entity\EntityInterface;
use Drupal\file\Entity\File;
use Drupal\paragraphs\ParagraphInterface;

function omitsis_modular_node_update(Drupal\Core\Entity\EntityInterface $entity) {
  if ('modular_page' == $entity->bundle()) {
    if ($entity->hasField('field_paragraphs')) {
      foreach ($entity->field_paragraphs as $paragraph) {
        $paragraph = $paragraph->entity;
        $style_options = om_getStyleOptions($paragraph);
        foreach ($style_options as $key => $value) {
          if ('background_image' == $key) {
            $fid = $value['fid'][0];
            $file = File::load($fid);
            $file->setPermanent();
            $file->save();
          }
        }
      }
    }
  }
}

function om_getStyleOptions(ParagraphInterface $paragraph): array {
  $style_options = [];
  if ($behaviors = $paragraph->getAllBehaviorSettings()) {
    if (!empty($behaviors['style_options'])) {
      $style_options = $behaviors['style_options'];
    }
  }

  return $style_options;
}