Issue with cached assets

Hi,
I have a problem with reloading css assets in a theme, no matter what I do, changes to the css file in my theme don't appear in the browser. I have disabled caching, twig caching, restarted webserver, clear opcache, deleted whole cache folder, but to no success.
I am running grav in vagrant on nginx with php 7.1.
The problem was mentioned on this forum more than once, but I tried everything suggested there and even reinstalled whole grav.

I am pretty stuck so thanks for any suggestions.

Can this be a problem of client-side caching of the CSS? Try opening the browser dev tools, with the option to disable cache.

Thanks for your suggestion, but this doesn't work either, i tried multiple different browsers, cleared cache, disabled it but no luck. When I check the network tab in chrome dev tools, it shows it has fetched the main.css file but somehow it has old content in it, not the new one. If I navigate browser to the location of the css file it shows the old content too.

Is it a public site? can I see it?

I am sorry but it is not, I have it in vagrant on my laptop. I am trying to go through the page loading with xdebug maybe I'll be lucky.

I finally figured it out, the problem that in the theme I am using the main.css file is not added through assets.add() function but with <link rel="stylesheet" href="main.css"> tag so it completely circumvents the grav core logic and stilll gets cached somewhere (I still haven't figured where). Thank you very much for your support @flaviocopes.

It seems I was a bit rash with the above solution, because it worked only for the first edit of that file after that the error repeated. After extensive googling I finally found the real culprit, it is a bug in vagrant with virtual box provider that breaks nginx sendfile function. So for development you should disable it in /etc/nginx/nginx.conf. With that you are ready to go.