The short explanation
Plug in an HDMI cable and four things happen in quick succession. The source puts +5V on the cable and the display answers by raising its hot-plug line. The source reads the EDID. If the content is protected, both sides authenticate over HDCP. Only then does the source start sending video, at the format it decided on.
Every one of those steps can fail, and the symptom is identical each time: no picture. That is what makes handshake problems so frustrating — one failure mode, many possible causes.
Where you run into it
The more devices in the chain, the more negotiations run at once. Source, AV receiver, switch, long cable, display: each is doing its own handshake, and one weak link stalls the whole thing. Swapping cables at random rarely settles it, because the failure is often intermittent.
The way out is to make the situation repeatable. Fix one variable — the EDID — and the rest of the chain becomes testable.
How the DR HDMI 8K handles it
The DR HDMI 8K gives you a fixed point in the middle of the chain. It reports RX and TX state, the FRL rate and both EDID sets live, so you can see how far the negotiation actually got. It can present a known EDID so the source stops changing its mind, and it can fire a hot-plug event on demand to retry the handshake without touching a cable.
Want to test your own HDMI chain?
The DR HDMI 8K is sold through the HDFury.eu web shop.