This isn't _strictly_ true - I've seen basically the equivalent of noise in a HDMI picture (white dots all over the picture), and eventually tracked it back to a faulty HDMI cable.
I did replace it with the cheapest (<£5) HDMI cable I could find though, so there is that.
Say the HDMI cable is crap and it can only do 100 packets per second, and HDR needs 1000 packets per second, the HDMI chips are going to negotiate a HDMI transfer settings without HDR. Going back further, say the HDMI data path is negotiated to do only basic HDMI, say, DVI-like video. If even that is too much for the cable to handle, say, it constantly drops a few packets, you would get either perfect pixels or missing pixels.
The only difference is the threshold.
Is there any error correcting code/protocol in HDMI spec to fix individual bit flips?
Displayport has packets with a checksum but I don't think there's any resending, only discarding.
" While the receiver may reach a determination sooner, the receiver must determine loss of synchronization at least by the time it has detected 50 consecutive data island packets with ECC errors. The HDCP Receiver must either assert the REAUTH_REQ bit of the RxStatus register or de-assert HDCP_HPD to the upstream transmitter once it determines loss of synchronization. "