The 'Home' is designed to show 1-day, 7-day, and long-term averages.
When you press the reset button, the device starts a new measurement and all previous measurements are deleted. This means that when you press the reset button you will need to wait 7 days before 7-day averages start appearing on the screen. Before the 7-day measurement mark, the 'Home' will only display 1-day and long-term averages.
Just let the device measure for 1 week and the 7-day averages will start to appear again!