vaapih265enc generate noise in some special picture with low power mode.
With cmd:
gst-launch-1.0 videotestsrc num-buffers=100 ! video/x-raw,format=NV12,width=1920,height=1080 ! vaapih265enc tune=3 low-delay-b=true rate-control=cbr ! filesink location=out.h265
Check out.h265, there are some green noise in gray and snow part: