If you are using "calc" autoptimize will make code that looks like this
calc(-50vw + 50%)
The problem being spacing in calc matters as the first rule is valid but the second one isn't. (I just noticed this on a client site I was working on).
cfr. 685d76b this should be OK on the GitHub version (which one day will be AO 2.2 or 2.1.1), can you try that @Volnus ?
Works closing the issue ^^