[Forums] CSS resource cannot be found

I have a Layout webblock Layout_SB_FullWidthLandingpage in module SB_Theme. I use this layout in another module say <consumer>.

On the Layout I have some CSS and some JS.

In the DEV and TST environment this works fine.

In PRD we have a problem. The JS resource can be found, but the CSS resource gives a 403, forbidden. So the layout of that screen is messed up.

See the attachment for some screenshots and observations.

OS 9, cloud