That is great! Sometimes flicking switches pays off!Thanks all for the suggestions. I should have mentioned earlier I've been running 4k HDR on multiple devices for a year with no problems, when all of a sudden it just stopped working inexplicably for every device. I called Sony ES today and resolved the issue with the tech. He hypothesized it was most likely an EDID handshake error and we resolved it by doing the following:
1. Change HDMI mode on the projector from Enhanced to Standard for both inputs.
2. Reconnect my devices; set resolution to 4k with HDR off.
3. Change the HDMI mode back from Standard to Enhanced.
4. Re-enable HDR on my device(s).
And just like that everything is running smoothly again. Hopefully this info might help someone else save some time in the future.