Drone crash due to ekf variance

My drone crashed while flying perfectly fine. When drone was coming back in rtl mode due to battery failsafe it started going in circular path and lost its altitude leading to crash. Can anyone help in solving the issue. Here is the log of the flight.

Here is the link of my logs:
https://drive.google.com/drive/folders/1sejgCuFzoDQ3w3zMLhKwYKtm4O7XhN6d