Because its data can become corrupt, so it is incorrectly reports avast as not running (when it is). This possible corruption is why Eddy was suggesting a Reset of the WAC/WSC.

Try this, right click the avast tray icon and select - avast! shields control - Disable for 10 minutes; you will get a confirmation dialogue, answer yes. Now restart the shields from the avastUI, this may jog the WAC out of its slumber.