I have a Flask app that relies on javascript for certain functionality. The javascript file loads fine sometimes and other times I get an error in the console:

GET http://localhost:5000/static/js/sm4sb.js net::ERR_INVALID_HTTP_RESPONSE 200

When this happens the javascript is not loaded. I then have to refresh the page multiple times until the console does not show this error.

I read somewhere that putting this in my config.py file should fix it, but it doesn't

SEND_FILE_MAX_AGE_DEFAULT = 0

Elsewhere someone suggested adding this:

@app.after_request
def add_header(response):
    response.headers['Cache-Control'] = 'no-cache, no-store'

But when I do that I get an error

AttributeError
AttributeError: 'NoneType' object has no attribute 'vary'

Note that the issue is with Vivaldi (Chrome) but does not seem to be an issue (so far) running in Firefox.