NUC6AYH : No-go for HDR.
NUC7i3BN : Works with HDR (on the previous build you posted about roughly a week or two ago)
That's interesting.
According to Intel's support pages for those NUCs they use the same MCDP2800 LSPCON chip.
Can you retest NUC6AYH with the build from post #502?
Also note that there is an issue with those builds. If you turn the TV off and then on (while the NUC is connected and working) - HDR will stop working until Kodi is restarted (maybe a bug in EDID parser code).