When tuning system for modpagespeed, http/2, PHP7 w/opcache, https, ran into issue with Apache, where turning modpagespeed off, then back on, or off then restarting doesn't clear cache. On a development site, I had to do a htaccess to fully disable in order to apply CSS changes which were 'stuck' -- a 'clear cache' option from panel would be super cool, vs command line ! :-)