Hey Tubal;
We just released Autoptimize 2.4 and it comes with the 4.x-version of this great CSS minifier. I have been able to confirm one bug that traces back to YUI-CSS-compressor-PHP-port;

.full-width-content .nectar-recent-posts-slider .recent-post-container .inner-wrap h2{font-family:Archivo Black;text-transform:capitalize;letter-spacing:0;font-size:60px;line-height:74px;font-weight:400;}

after minification becomes:

.full-width-content .nectar-recent-posts-slider .recent-post-container .inner-wrap h2{font-family:Archivo #000;text-transform:capitalize;letter-spacing:0;font-size:60px;line-height:74px;font-weight:400}

so font-family:Archivo Black; becoming font-family:Archivo #000;

This was not the case in AO 2.3.x which still used the 2.x version of your minifier. Could you have a look at what is happening here?

Thanks!
frank