Resolve long initial load time in large ReactJS application using a service worker

I have spent many hours trying to resolve this issue and I am at a loss for what to try next. My React application takes 6+ seconds on the initial load which is not great as a first impression.

I have structured my application well, am using lazy() on pages and some of the larger components and code splitting is working as intended. However, on the first (ServiceWorker) request there is a huge delay of ~5 seconds.

What is going on here? How can I further debug this request?

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