Ok, after manually editing the service worker and removing the offline fetch event code, the errors went away. Then, I cleared all caches, app data, cookies, etc. Then, I deactivated and reactivated the extension.
Now, all seems OK. 🙄
Therefore, to those above who have ever experienced similar issues: I think it is just the nature of PWA and browsers. You will have to mess around emptying things and even possibly manually, temporarily, change the service worker. Maybe this helps the browser to think there's something new. You may have to continue trying things like this for a good hour. Haha! But, eventually, everything syncs back up. 😀
(I still think public assets folder for Flarum is a little buggy.)
