There are times when it seems your device has a mind of its own, and won't work consistently - it may not even do the same thing the same way from one time to another.  One of the first things we suggest is to do a full hard shutdown.  A hard shutdown is different than simply closing the top cover or pressing the power button.  Those two methods simply put your Chromebook to sleep.  Sometimes your device just needs a full, fresh reboot.

To perform a Hard Shutdown on the Chromebook:

Hold down the Refresh image key and the Power key at the same time for 4-6 seconds to shut the Chromebook completely off.

Power the Chromebook up, login and see if the problem is resolved.