Gaps in Waterfall

I searched through and found a few other threads on this topic, but unfortunately nothing really cleared it up for me.

I’m seeing small (and sometimes large) gaps in my test results. Often the CPU Utilization is maxed out during these gaps, so it seems like the site is trying to do something.

Here is an example I just ran:

I’ve also attached some other interesting screenshots that also illustrate this.

I’ve seen recommendations for using the tcpdump and netlog, but when looking at those files, I really can’t understand them.

I am using HTTP2 Server Push as well as a Service Worker on this WordPress website.

When I view/time the website myself, it loads as fast as a quarter of a second on repeat view, but WPT is reporting 4.5+ seconds for repeat view. I’m just trying to understand this a little bit more to see if I can find what to focus on next to optimize more.

I’m happy to provide more data if needed.