Hi Frank ~
Well that's something i wouldn't have thought about - that it may be working anyway despite the CSS looking mangled. Since my stylesheets do begin with @charset "utf-8"; on the first line, that makes some sense.
I will check and see if maybe it's working fine. But first i have to resolve two other issues with Autoptimize actually breaking things. One was already posted here at :
https://wordpress.org/support/topic/conflict-with-fancybox?replies=7