After pushing a dev instance of drupal to a server, the admin CSS broke.
Browser Console showed *.css files that were obviously auto-generated, but no amount of browser cache clearing, CHMOD, or D8 cache clearing resolved.
Here's an excerpt from the D8 forums - with the actions that were taken noted with ***
The method that has worked for me in past is below:
There may be an unneccessary step of two , but I prefer safe over sorry.