We upgraded a site from 5.4.2.2 to 5.6.1.1 (stepping version by version) and now the site's styling is shot.

Even with caching completely disabled the site is looking for the style files in /files/cache/css/theme_name/ but at first the css files there were 0 byte. The images folder was never copied over.

I've tried clearing and disabling the cache, no joy. This process wiped the files, but didn't recreate them. All styling is gone from all pages.

I tried forcing the 5.6.1 upgrade script again and that helped for about one page load - then back to broken.

I have things running for the moment by manually copying the css files and images to the cached css folder, with cache still disabled. It's holding for the moment but that's not a long term plan.

Possibly related: The site can not connect to the Marketplace. It says marketplace connectivity is disabled in the config file ... but it's not. However, if I explicitly enable it, the marketplace connection works.

This was a fresh, unedited download of each version of C5 we stepped through.

FWIW: This is at least the second site where this has happened. The first one is no longer a client (they switched to a different platform).