since we upgraded php to 7.1 the request for "index.php?module=Proxy&action=getCss" fails with an error 500, resulting in no css being loaded.
Testet in a new site, with nothing in it except for piwik, with the following versions:
once we switch back to php 5.6 it works again
Do you see any errors in the error log running php 7.1?
no, no warnings or errors in the php-logfile