Problem: Mobula6 (Crazybee F4 Lite) flight controller settings have all been wiped, and the SPI receiver has lost bind.
Sometimes if your battery gets over discharged (below 3.0V) and you still try to fly your quadcopter by running the motors it can actually cause a power brownout on the MCU that causes the EEPROM to get corrupted.
This results in all the user saved settings to be cleared on your flight controller.
For now you will need to connect to your FC and set all the parameters onto the flight controller again. This includes configuring the RX and binding it again, setting up your flight modes etc. Alternatively you can also just load the CLI dump for your particular board version for Happy Model.
Happymodel are working on a permanent solution to this bug, but for now its best to set a low voltage alarm and make sure you land before the voltage drops too low. If it does, do not move your radio sticks to try prevent this from wiping your EEPROM.