I finally understood that the build settings “data caching” should be disable to let the server/browser cache work as expected.
I was assuming if data chaching was disable it was reloading from server each time, but absolutly not. As @AgnosiaGames pointed it out when this option is enable it’s unity that handle the caching file. In some case this is what we want but not in general.
More info about how work the cache settings can be found here: WebGL Settings Data caching?