Do you experienced lagginess when using pop-up play? I played an HD video and it laggy like you are on power saving mode. But the lag stopped after maximise the pop-up play. Seems to only effect when it is not in full-size. A few lags here and there at times. I'm using 64GB SanDisk class10 card and formatted to exFat. Was running better with Fat32.
Weird thing is if you use the phone to format the Card, it will format to Fat32 instead of exFat.