It's probably the pixelation of the image while flying due to the lag and latency of the WiFi being interrupted momentarily.
Most noticeable when flying via WiFi connection to the device.
I use to fly via WiFi because it was hit or miss if the OTG cable worked with the Spark during the "supported" or " not supported" history of the Spark.
But I have found that the OTG cable is a better to use as it's a solid connection between the device and the remote.
I haven't had any lag, pixelation, or Bluetooth warnings since using it.