I also suspect that it is a hardware problem for me too: I thoroughly investigated the problem of sending the video signal to my display (a Panasonic PDP 55VT60, therefore simple 1080p), and I realized that the passthrough block is not THE problem, but only a consequence of the problem. Basically, something leads to the AVR20's output video being turned off after putting it into standby. Just wait a bit, and at that point if you were using the AVR in passthrough the video disappears (letting the audio pass instead), but even if you were not using the passthrough function when the AVR was first turned on it is impossible to have the video signal in the plasma. You only have the audio, but the screen is black, and there is no way to solve even switching between inputs. The AVR is really blocked, in fact it doesn't even automatically switch to the Display input, when I set a TV channel via the plasma remote control, it's just as if the HDMI video card is blocked. And this happens even if I turn off the CEC completely in both the AVR, the sources and the plasma. So it is not even a question of communication problems between the various HDMI EDIDs of the electronics involved.
The only way to unlock the video signal is to power cycle the AVR, or to reset to factory. Even browsing for a few seconds in the menu on the front panel, using the appropriate MENU key, seems to be useful, but I want to verify it with certainty, since it could also be just a coincidence (I discovered it a little while ago, but I want to repeat the test at next AVR block).
Of course, if ARCAM's assistance times are those you have indicated above, for me who am in Italy they will be even longer ... and having a real replacement I think it will be difficult for me...
Ettore