I encountered a special case where my CSS broke after minification. I made a JSFiddle wich shows the issue:
https://jsfiddle.net/yn1ypvg9/2/
Issue is the same in Chrome, FF and IE (11)

the first block is the non minified version, the second block is the minified version.
As the "::placeholder" pseudo-selector is not recognised by the browser (because it is still experimental and only works with vendor prefixes), the entire block of css is ignored.

I'm not sure if these scenario's can be fixed because it seems to be a general way of interpreting CSS across browsers and you can write anything that is not recognised instead of 'placehoder", it will result in the same issue.