Update: It was because the hosting had a memory limit. They increased the limit and it fixed the issue.
$del_id = implode(',', array_map('intval', array_map( 'sanitize_text_field', $_POST['del_id'])));
I confirmed that this works at least on my localhost. Thanks @vermillionone good job!
You shouldn’t be editing plugin files directly. I’d like to see someone come up with an answer that isn’t editing the plugin files.
