We had the same issue today. Isolated several variables and confirmed it only happens when caching Netlify sites through Cloudflare. It replaced not only our CS

We had the same issue today. Isolated several variables and confirmed it only happens when caching Netlify sites through Cloudflare. It replaced not only our CSS file, but all cached assets included our homepage, images, videos, .js files... Took down our entire site and the only way to fix was completely disabling caching through Cloudflare. Seems like to me that it is a Netlify issue that is responding incorrectly specifically to CF's servers, but it's also possible it's a Cloudflare issue. We literally just moved our entire site over to a backup server temporarily until we can get it figured out.