The standard setting is 444, 8bit - not 420.
YCbCr 4:2:0 is not officially supported by the HDMI standard (except for 2160p50 and 2160p60).
However, it might still work in some cases.
If i boot my box without autostart.sh, my AVR say's 420 8 bit. But just to be sure, i'll check it again later on.