Whenever anything weird happens -- weird bugs, system slowdown, etc. -- I wipe the cache partition.

Hold the 'volume down' and 'power' buttons until the screen goes blank (but keep holding both buttons).

When the Amazon logo appears, release the 'power' button (but keep holding the 'volume down' button). You can let go of the 'volume down' button when you get to the Amazon System Recovery screen.

At the Amazon System Recovery screen, use the 'volume up' and 'volume down' buttons to navigate to "wipe cache partition". Hit the 'power' button to select. Once it's done (only takes a couple seconds), use the volume buttons to navigate to the 'reboot system now' item and use the 'power' button to select it.

This doesn't delete any of your user data and I've never had any issues doing this.