Site slow loading in AM, normal in PM!?

I thought I got hacked based on the subject “site slow to load” in the FAQs. However, on afternoons and evenings my site loads normal. Just as I was about to re-install WP, my files and database, my host support told me that my site loads normal on his computer.

I started experiencing this since last week when I downloaded Yoast SEO to support Google analytics. Could this plugin be the culprit?

To those before me, is this “security challenge” the last normal hurdle that a WP blogger needs to go through? Thanks.

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