If your Rocketbook erased itself by being exposed to extreme heat, have no fear! Your writing can be recovered!
Pilot FriXion ink operates by turning clear when exposed to increased temperature due to the friction of the eraser on the page. However, the ink can be erased through any exposure to heat, including warm water, a hot car, or even fire! Pilot FriXion pen ink turns clear at 140°F/60°C and regains its color at 40°F/4°C. Please note that this only happens with the Pilot FriXion pens.
In order to recover the erased text, leave your notebook in the freezer for a few hours. Cooling the pages below the 40°F/4°C threshold should restore the pigment of the ink. Also note that when you wipe down a Core (formerly Everlast) with a moist cloth, the ink is removed from the page, so you don't have to worry about old ink reappearing in the cold.