I followed the recommended steps above - the only change that was needed was changing the BOOT_ORDER value from 0xf461 to the specified 0xf416
The Pi boots into Home Assistant OS on the SSD as before, and every 2-3 reboots it still gets stuck in the inability to boot. This time it shows a friendlier screen showing that it is looping through NVME then SSD then USB (as specified in the BOOT_ORDER setting), but it never succeeds. I can power down the device and reboot and it will work to get to Home Assistant.
Then repeat reboots and the second or third time it will land in that boot loop where it doesn’t seem able to recognize a boot device.