Issue with CSS calc

That’s weird, there’s logic in the minifier to explicitly prevent that. I just did a quick test (with dummy CSS) and spaces are kept actually @jordanwebdev;

in:

.futtta{
	width: calc(16.66667% + .9375rem)
}

out:
.futtta{width:calc(16.66667% + .9375rem)}

so I _think_ AO is falling back on an already loaded CSS minifier (from another plugin?) instead of using the one AO comes with (it does if (!class_exists('CSSmin')) { before loading the minifier class, cfr. https://github.com/futtta/autoptimize/blob/master/autoptimize.php#L208-L210. So do you have a plugin (or theme) that has a CSSmin class loaded?

Alternatively you could try AO 2.4, which uses a much improved version of the CSS minification component and which loads the classes differently. You can download the beta-version here.

frank