Did some quick tests today with both our AltitudeCI and 16 (both HDMI 2.1 board, inputs set to 2.1). Between the Christie M-4K25 projector (HDMI 2.0) and the Trinnov output 2 sits the Envy Extreme MK2. All devices in the rack connected via Kordz 8K cables. The connection between the Envy output and the Christie is a CelerityTec HDMI 2.1 full-fiber cable.
OSD on the K was set to "auto" which set it to 60hz 3840x2160. I tested with 4KC DV, 4KC HDR10 and 4KC SDR content.
With both Altitudes, I got an immediate, stable connection. Switching back and forth between the OSD and movie content (I also played the 8K demo clip).
However, when I turned the system down and up again, I got just a black image on the projector. It seemed as if the chain was really outputing a black image, as I didn´t see a "no signal" message neither from the Envy, nor the projector. I could also see the K OSD on my preview monitor which is connected to the bypass port of Envy.
Both the Envy and the Altitude (CI in this case) reported a valid incoming signal (checked via the Envy IPControl tool).
A reboot of the Envy resolved the issue and I got the K OSD on both the monitor and the projector.
So in my case, the Envy seems to be the issue. Especially with the observation that the output port was outputing an image.
Unfortunately, I don´t have any more time to do more troubleshooting as the units I have here are already sold again.