[RZ/G1H] Noise ocuurs in video with gst-launch-1.0

I'm trying to scale and display multiple videos on RZ/G1H(iWave RZ/G1H-PF development kit + version 4.4-CIP Verified Linux Package).

But,sometimes the bottom of the HDMI output video blinks black. I attached the image.

[Command]

#gst-launch-1.0 -ev videotestsrc ! video/x-raw,width=256,height=192,format=NV12 ! videoconvert ! waylandsink position-x=800 position-y=0 qos=false &

#gst-launch-1.0 -ev videotestsrc ! video/x-raw,width=256,height=192,format=NV12 ! videoconvert ! waylandsink position-x=1056 position-y=0 qos=false &

#gst-launch-1.0 -ev videotestsrc ! video/x-raw,width=256,height=192,format=NV12 ! videoconvert ! waylandsink position-x=1312 position-y=0 qos=false &

#gst-launch-1.0 -ev videotestsrc ! video/x-raw,width=256,height=192,format=NV12 ! videoconvert ! waylandsink position-x=1568 position-y=0 qos=false &

(Omitted)

#gst-launch-1.0 -ev videotestsrc ! video/x-raw,width=256,height=192,format=NV12 ! videoconvert ! waylandsink position-x=1568 position-y=576 qos=false &

Do you know how to resolve?

Regards,

Yama