Hi,
I am afraid that is not possible. Its on a private sandboxed server with no external access. If you could give me any hints what to look for that would be good.
Or maybe @sonneundmond can provide access to their site and if you find a solution share it.
So to recap:
1. The option is enabled
2. I can see that the files are correctly generated on the server
3. Front-end ignores it and serves all other files individually.
4. WP 4.9.6, PHP 7.2, gzip compression enabled, Enfold 4.4.1, All other plugins on the site disabled including caching.
@sonneundmond: Yep, same here. Files are being created just not used.
(I get the exact same behaviour on other themes so it could be a server-side related issue.)