1. Make sure the Date Stamp is OFF: OSD Menu > General > Date Stamp > [OFF]. When the Date Stamp is ON, the lantency of the video out will be increased.
2. Split's input current could be not enough with the decrease of battery voltage on the flight. If PDB/BEC/FC/VTx can't supply enough current to Split, this issue will happen. Split's average working current is about 650mA. So please make sure input current is enough for it to work normally. It is better to power your Split via BEC(5V >=1A) / PDB 5V >=1A / FC 5V >=1A.
3. Ribbon cable may don't connect well. Unplug and replug the golden fingers of the ribbon cable and reinforce the joint of the 2 ends of the ribbon cable with adhesive tape.
4. The speed of the SD card cannot meet the requirement.
Which type of microSD card is fit for RunCam Split 1/2/Mini?
5. Try to change the TV MODE to NTSC and choose resolution: 1080p 60fps.
6. Try to power your Split by USB TVOUT cable and get the video signal via tv out as well.