Pace XG2v2 STB
Yamaha RX-V383 audio receiver
Optoma HD33 projector
Pace XiD-P STB
It is worth noting that all of these support HDCP 2.2.
If I plug the STB HDMI cable into the receiver, and the HDMI out from the receiver to the projector, the STB will crash as soon as I switch to that input. After that, when I switch away from that input, or turn off the receiver, the STB reboots. If I don't turn off the receiver or switch to a different input, the STB freezes indefinitely. If I let the STB reboot, it will crash again if I go back to that input. The behavior is the same on both of the STBs shown above.
If I bypass the receiver and plug the STB HDMI directly into the projector, it works fine. In that case, I need to connect an optical cable from the STB to the receiver, as the projector has no sound.
If I pass the HDMI from the STB through the receiver to an older projector (720p, no HDCP 2.2), it works fine. If I pass the HDMI from a different source (e.g. Chromecast, or my Dell laptop) through the receiver to the Optoma projector, it works fine. When I had an older STB it worked fine, but back then I was passing it through a different audio receiver.
I tried switching to different HDMI inputs on the receiver, different HDMI input on the projector, using different HDMI cables, and it made no difference.
I tried one really complicated experiment to figure out as much as I could. I connected the HDMI from the STB into the receiver, being careful not to switch the receiver to that input. I also ran a yellow composite video output from the STB to the projector, and switched the projector to that input. I also ran an optical cable from the STB to the receiver. So then I could see the TV picture on the screen, but it was low quality through the yellow composite video. I could hear the sound through the optical output into the receiver. I brought up the STB menu using the remote, and I could see the box was responding normally and showing the TV channel behind the menu. So far so good. Then I switched the receiver to the HDMI input from the STB, and it was still good. I was getting the audio from HDMI, but still showing the video from the composite input on the screen.
Then I changed the projector input from composite to HDMI, and everything died. Both the sound and the video cut out immediately. I gave it a good amount of time to handshake the HDMI, but nothing. I switched the projector back to composite video input, and saw the STB was frozen. I could see the menus, and the TV picture was still actively running behind the menu. But the menus no longer responded to input from the remote, so it was clear the software had crashed. Then I switched the receiver back to the optical input to see if there was any sound, but that immediately triggerred the STB to reboot. It rebooted cleanly, but then when I again tried to switch to HDMI the same thing happened.