Please check the below three aspects:
1. Current input to split;
Please power up the Split via USB by a phone charger (5V 1-3A) to see if it works properly. If it does, it indicates the problem is caused by insufficient power. Please then try to change your power setup to PDB/BEC/FC 5V/12V.
2. Make sure the battery is stably connected.
3. You may also try another card, please refer to Which type of microSD card is fit for RunCam Split 1/2/Mini?