Tried hard-refreshing by Ctrl + R and disabling cache by Chrome developer tools > Network > Disable cache but it’s still not serving the latest version of static files (.css, .js) I just uploaded.
It turned out to be CloudFlare.
So I enabled developer mode at CloudFlare for 2 hours and it’s working fine now.
Another solution is to add a trailing ?v=1234 to the end of the static file for each update to force CloudFlare to cache the updated version.