My guess is they've been serving their css file direct from disk with no content encoding header, but browsers rolled their eyes and decoded it anyway (do they

My guess is they've been serving their css file direct from disk with no content encoding header, but browsers rolled their eyes and decoded it anyway (do they do that?). But now it's changed to serve behind a reverse proxy which isn't so forgiving and recompresses it with brotli (does it even reduce the size?) and that's too much for the browser to infer implicitly. Fin.