Service Worker mishandling user login on App Engine - google-app-engine

Question

I'm having a particular problem with my Service Worker in conjunction with my Google App Engine app. The service worker installs and activates perfectly. Also, I used the exact same service worker in another app that I built (which didn't require any user login) and it worked fine. However, on my current app, there is only one page (App Engine renders the page and sends it on successful login using the built-in user API). My problem is that I don't want the root address, a rendered page from the server, to be cached. Here is my files to cache array:
var filesToCache = ['/manifest.json','/js/app.js','/js/jquery-3.js','/js/jquery.matchHeight.js','/js/materialize2.min.js','/js/vue.js','/js/vuex.min.js','/js/chart.js','/css/materialize.min.css','/css/style.css', '/images/case.jpg'];
As you can see, I'm only trying to cache the scripts, since the HTML must be rendered server-side, and it is extremely compact, so I don't mind the small network request to be made. And here is my service worker which resides in the root folder.
self.addEventListener('install', function(e) {
console.log('[ServiceWorker] Install');
e.waitUntil(
caches.open(cacheName)
.then(function(cache) {
console.log('[ServiceWorker] Caching app shell');
return cache.addAll(filesToCache);
})
.catch(function(e) {
console.error(e);
})
);
});
self.addEventListener('activate', function(e) {
console.log('[ServiceWorker] Activate');
e.waitUntil(
caches.keys().then(function(keyList) {
return Promise.all(keyList.map(function(key) {
if (key !== cacheName) {
console.log('[ServiceWorker] Removing old cache', key);
return caches.delete(key);
}
}));
})
);
});
self.addEventListener('fetch', function(e) {
console.log('[ServiceWorker] Fetch')
e.respondWith(
caches.match(e.request)
.then(function(response) {
return response || fetch(e.request)
})
);
});
The problem is, despite the fact that I don't try to cache the root address, the service worker will try to return a response instead of a fetch for a user's initial try. This is the sequence of events after a user navigates to the app:
1 - Landing page with button showing 'Sign into Google'.
2 - Redirect to app upon successful login
Expected Result: user is redirected to Google's own solution, after which, the user will be redirected back into my app fully logged in.
Actual Result: service worker intercepts request, serves undefined response, redirects user back to login page ad infinitum.
I'm pretty new to service workers, so perhaps there is something in missing in intercepting response and some edge case I need to account for, but I'm not sure what it is. I've tried splitting up the return statement to first check if there is a response, so if the response is undefined, it skips the return response statement, cloning the event, and then returning the event request in a fetch request. However, I got exactly the same result.
Has anybody come across this before or know what to do? I spent all yesterday on this to no avail and just gave up on returning any response at all, serving everything from the network, but I really want to solve it. Thanks for any help in advance.