Some watch notifications could be the main cause. In order to resolve this, get into the habit of dismissing or answering your watch notifications. If a notification hangs out for too long on your watch, eventually it may self-dismiss and revert to your stock Apple Watch face. Navigation, auto-launch audio apps, and covering the display with your hand are also main reasons why Clockology will get sent to the background.  Removing your watch from your wrist will also cause Clockology to run in the background.