Thank you for letting me know.
I have already fixed that.
Next version you will get it fixed.

There are lots of hooks in this plugin and you can change almost anything without changing core plugin code.
It is not recommended to change plugin code.

after that also if you need, this fix is located in class-fep-pro-to.php

Thank you for letting me know. It it happening due to object passed by reference.
It is already fixed. Next version you will get it fixed. If you now want to change code please go to class-fep-pro-to.php line 536 and change foreach loop with this foreach loop

foreach ( $this->first_message_attachments as $attachment ){
	$attachment = (array)$attachment;
	$file = get_attached_file( $attachment['ID'] );
	unset( $attachment['ID'], $attachment['guid'] );
	wp_insert_attachment( $attachment, $file, $message_id );
}

Let me know. Also let me know if you find any more issues.