Problems with media player on Samsung 55NU8000

snadge

I have a Samsung 55NU8000 and an Android Box with a RK3399 chipset connected with HDMI, when I set the box's output at 3840x2160 50p or 60p the screen flickers on and off, if I set it at 25p or 30p it works but has severe micro stuttering (worse with motion plus enabled) - at 24p it works fine on local video files (even with motion plus enabled) but when I stream on BBC iPlayer and other apps it has micro-stuttering occurring randomly a few times a second

does anyone know why this may be happening?

thanks in advance