I debugged queries and performance using Query Monitor. Im posting the results with permission of dreadcentral with site-specific info redacted.
Before.jpg is the performance of your #1 page with our plugin disabled. There are a total of 235 queries.
After.jpg is performance of the #1 page with our plugin on. There are 236 queries. Only one more.
Checking query details, Slow.jpg shows that there are 4 slow sql queries which in total add a ~1.5 sec to query time, which would also cause high cpu spikes.
These are not related to our plugin. It seems your theme is pulling related posts from the same category and showing them under the post being viewed. This means that ~4 more times everything related to a post will run in every one of your single post pages - because you show 4 posts in one go.
Long story short this is a situation with your related posts plugin or related posts functionality that is built into your theme. If you show 4 posts in one go while showing a single post, anything related to posts will be called 4 times - naturally.
Speaking of the theme/plugins:
Warning.jpg shows that there is an issue in code relevant to a query which gets next/previous posts (probably to show them in your single post page), that causes a warning to be given by WordPress core. The code causing this seems to be in your theme - Zox News, inside its single post display template single.php. Line 383.
I advise against changing the theme or doing major changes to the theme since this could affect your SEO ranking for your popular pages. However the code that causes the warning must be looked at first.
I wasnt able to notice any notable change in total time the queries take. With our plugin disabled, or enabled, it seems to take in between ~1.1 seconds and ~2.5 seconds randomly.
Summary; this seems to be related to your theme displaying 4 posts in one go while showing 1 single post. Any plugin that uses the_content filter will kick in 4 times with this setup.
We can see if we can do some optimizations on our end, after you have that PHP warning looked at.
For the time being, you can just drop the below code to your theme’s functions.php or any plugin to disable image protection: