I have a Z2 that is intermittently experiencing this issue. It seems to occur when I have a lot of apps open (but closing them does not help~. I'm trying to get the handset replaced as it is unusable like this.
XDA Developers was founded by developers, for developers. It is now a valuable resource for people who want to make the most of their mobile devices, from customizing the look and feel to adding new functionality. Are you a developer?