Each alternate Wacom stylus stroke drawn in quick succession (using any tool) was not getting captured and hence the selected tool appeared to be working intermittently. 

For example, when you use brush tool and paint brush tool, rectangle & oval tool, paint brush, and paint bucket tool. 

This issue was not observed when drawn slowly or while using mouse.

Solution

To fix Animate time-lag issue with Wacom, update the Wacom driver to the latest version.

For more information, see Wacom device drivers