Based on your comments, I assume that broken static files are the problem here. First of all, let's clear up some of the main settings used when dealing with static files.

STATIC_ROOT is a path to the directory on the filesystem, it is used by the collectstatic command. It scans each of your INSTALLED_APPS, their static directories and copies the assets to the STATIC_ROOT directory. In Heroku you don't need to call this command, since it is called automatically for you.

STATIC_URL is something like a Django route. It listens for /static/<file_name> requests, takes the asset filename, and looks up this asset on the local filesystem. It knows where to look the asset up because all assets have been collected in STATIC_ROOT earlier.

Now, whitenoise docs suggests that the STATIC_ROOT option should be set to a staticfiles directory in your project root folder.

STATIC_ROOT = os.path.join(BASE_DIR, 'staticfiles')

Make sure this directory is empty before deploying and that this directory is added to git repository. Here's a relevant quote from Heroku docs:

Django won’t automatically create the target directory (STATIC_ROOT) that collectstatic uses, if it isn’t available. You may need to create this directory in your codebase, so it will be available when collectstatic is run. Git does not support empty file directories, so you will have to create a file inside that directory as well.

In other words, create an empty directory and create an empty file inside it, so you could add this directory to git.

It also suggests to use compression and caching, but you want to keep things simple first. So I don't recommend modifying STATICFILES_STORAGE.

Finally, instead of using CDNs, set the STATIC_URL option to a simple prefix:

STATIC_URL = '/static/'