Plugin error while creating posts

Hi everyone. It’s my first time using this plugin and i got this error

[Sun Jul 07 21:09:00.802654 2019] [php7:error] [pid 5156] [client ::1:52160] PHP Recoverable fatal error: Object of class WP_Error could not be converted to string in /home/user/www/html/wp/site/wp-content/plugins/wp-lorem-ipsum/lib/class.posts.php on line 37, referer: https://localhost/wp/site/wp-admin/options-general.php?page=wp-lorem-ipsum

Code reference:

php
Class LiPosts::get_attachment_id_from_src()

$query = "
  SELECT p.ID
  FROM {$wpdb->posts} AS p /* at this line*/
  WHERE 1=1
      AND p.guid ='{$image_src}'
";

Config used:
Number of posts: 20
Post Type: Post
Post status: publish
Post Author: [My User]
Post Thumbnail: true (checked)

However, 7 posts were created at my database even with this error
I tried to reproduce it but with no success (still throwing the same error but without creating anything)