If you are running NGINX or Apache within a Virtualbox using Vagrant, you may encounter unintentional, persistent caching within the webserver. If so, try turning off sendfile.
This is due to a bug/issue with the sendfile syscall (h/t @mitchelh) that servers typically use to serve static files.
It’s solved with a webserver configuration option:
Apache
EnableSendfile Off
NGINX
sendfile off;