What does things all went south mean in the following paragraph?
The app has been available in the Google Play store since November 12, apparently with Google's blessing, and Cyanogen says "hundreds of thousands" of users have installed it already. But things all went south on Wednesday, when the Cyanogen team apparently received an email from the Chocolate Factory informing them that the CyanogenMod Installer violated Google Play's terms and conditions.
I'm really confused by what this idiom means. Kindly help me out.