There's a bug in Virtualbox that results in small, static files not being transmitted over shared-folders properly. This purported solution is to add "sendfile off;" to the server/location block in Nginx (or a corresponding fix to Apache/etc...) and reloading. This prevents gibberish from being received in your Javascript, CSS, etc..
However, it's not working for me. I'm definitely hitting the right server/location blocks, but, even after reconstructing the Vagrant instance (with the Virtualbox provider), I still get gibberish in my files.
Does anyone have any guesses at what could be going on?