Before take-off the image transmission is OK, I can move the mavic-air in any direction and see the image moving on my  Iphone.
After take-off the image freeze and the message “non image transmission appears”
Does someone have a solution to my problem?  

Hi there. Thank you for reaching out and we're sorry for the trouble. Can you please confirm if you are using the DJI Air 2s or the DJI Mavic Air? In addition, could you please try to calibrate your IMU and please try to fly to a different location to see if the issue persists? Please keep us posted. Thank you.