I'm no expert at either HDMI or HDCP but I believe that in order to advance this discussion, we need to separate the physical wiring standard (HDMI) from the communications protocol standard (HDCP). Again I don't know for sure but having read some of the threads, I believe that most of the interconnect issues that the OP mentions are most likely the result of failures of the protocol between devices. Anyone who has studied successful I/T or communications protocols knows that you need to have a mechanism for understanding what went wrong when something doesn't work as expected .. and that seems to be a fundamental flaw in HDCP .. the user has no idea why things don't work.
If this was an I/T system, you'd just dive into the error log; look at the handshakes; and figure it out .. but there is no HDCP 'error log' that I know of that you can consult to try to understand why the handshake is failing. Ideally, someone needs to create a small, preferably handheld HDMI to HDMI device (that you could buy at BB or your favorite retailer) which you could insert at any connection point that would 'watch' the protocol flow for anomalies and then output an error code that you could look up in the chart that came with it (or online) which would be the best guess as to why the handshake failed.
This wouldn't be a 'repeater' as much as it would be an 'inline sniffer' and diagnostic unit in one. It wouldn't be like the auto OBD II diagnostic machine because OBD assumes that your car has already saved some error states that the diagnostic machine just analyzes .. in the HDCP scenario, I don't believe there are any 'error codes' saved anywhere .. and even if they were, they'd likely be inside a component (AVR; UHD player; projector; etc) and you'd likely need a brand engineer to extract them. What I'm suggesting is a device which analyzes the flow in real time and attempts to diagnose what the likely cause is. I think the communications industry has tools like this that they've been using for years although I don't know if they're using them to look at protocols (eg. TCP/IP).
The beauty of something like this is that you could plug it in at either end of any cable in the chain so you if you had a UHD player connecting to an AVR outputting to a TV, you could determine whether the protocol failure was between the player and the AVR or the AVR and the TV. Plus you could determine that the AVR was "within protocol spec" at the AVR output connection but at the other end of the cable (TV or projector), it was not within spec. I think only a couple of the many twisted pair with the HDMI connector are used for protocol so it's not like the 'device' would need to monitor a huge number of cables ... and if I recall correctly, the pair or two that are used for HDCP handshakes are at a much lower freq than the 3 that are used for the actual video signal so likely easier/cheaper to monitor. However, to diagnose the sync/desync issues mentioned earlier, you might need a more expensive/capable device to do that as well (the 'deluxe version') although that may be more for industry integrators rather than typical consumers. Heck, maybe even the simple one might be too much for typical consumers .. but I bet people would pay to have the BB Geek squad come out and figure it out for them. Maybe places like Magnolia could offer that as 'part of the deal' to avoid returns.
My recommendation would be to convince the HDMI organization to work with an electronics developer to bring this to market. The developer would design the device; manufacture it; and make it available to the market and HDMI org would provide the expertise on the protocol symptoms and what the most likely error condition is. That way you wouldn't have to deal with all the AV vendors out there plus HDMI gets to put some teeth in whether or not their protocol standards are being met. If vendors are toeing the line, they get called out by the device. Assuming it's an HDMI implementation problem (as opposed to a bad component), the vendors could probably fix it with firmware the same way they do today. If it's a cabling issue, you can probably return the cable and get a different or better one. If it's a length issue, then you move the source closer to the target or invest in a technology which gives you longer length.
No sooner had I posted this than I discover that someone already builds a similar device: http://www.murideo.com/analyzers.html
which appears to be way more than I was asking for (eg.does HDR) and is probably for professionals with a professional price. Now someone needs to scale it down in function and price to something a serious AVSer can afford.
Edit2: Or maybe we just need one of these upgraded to HDCP 2.2 and UHD: https://www.hdfury.com/shop/otherhdf...dware/dr-hdmi/