Weird caching issue

How to reproduce:

- Open incognito;
- Go to https://www.freereikicourse.com/advanced_practitioner_level_2_12.html
- You will see **no flicker**
- Refresh any other page and starts flickering.

I think the service worker or something like that is caching the homepage and serving that html for all other pages.

In addition to this problem, the first time it loads "https://www.freereikicourse.com/advanced_practitioner_level_2_12.html" it redirects to "https://www.freereikicourse.com/advanced_practitioner_level_2_12.html/" slash at the end. After the first time it doesnt happen again.

Obviously something is messed up.

"In production, we register a service worker to serve assets from local cache." That is a great feature, but doesn't work well..

Start by reproducing the two URL behaviors in an incognito browser, then inspect the production service-worker registration and its asset-cache handling. Done means each page serves its own HTML without flicker, and the first visit no longer gains an unexpected trailing slash.

Written by the indexing model from the issue text.