Sorry for the late reply!
You are the first person to report this; I don’t use chrome much but haven’t noticed this bug. I have no clue on why this would even happen.
I do have some chrome visitors on my blog I know and chat frequently, and they told me the css was working for them.
Anyways, I have filled a bug for this issue on Autoptimize’s tracker and will try to reproduce it when I get some time. The bug link is here: https://bugs.launchpad.net/autoptimize/+bug/612774
It would be very useful if you could provide me with a link to your blog running autoptimize, and if you could answer this simple questions:
1- does the css work on other browsers? (IE, Firefox, Flock, other webkit-based browsers like Safari and Midori, etc)
2- Does it still happen after cleaning both autoptimize’s (on the options page, use the white button on the bottom to clean it) and your browser’s caches?
Looking forward to hearing from you!