I just repeated your simulation,
You probably left the "Realistic" option "ON" for the Sun, if so, then decreasing the mass to 0.9 Suns decreased your Sun's Luminosity to 0.54 and that is what froze your Earth.
Suggestion to GA: please highlight somehow those parameters that got altered dynamically due to a manual change of another parameter. Maybe a 5 second colour change or blinking?