Sorry for the inconvenience caused. I can share a tip with you. Go to Schedule ->History ->find the historic task with your whole house->click it and click "Use" on the top right corner. Your map will be back.
You can watch this video to see how to do that : https://youtu.be/pr-UY2W-InI
The map disappears when radar cannot recognize the surroundings. Any move of furniture might cause this problem. It usually happens when you move your robot to another place then hit the spot cleaning button. I would suggest you always starting cleaning tasks while the robot is on the charging station. Another common error is people move the charging station, which causes the robot get lost.