Yes. The monitor behaves exactly as you described. However  the amber light turns to solid insted of blinking when the monitor goes to standby mode. When you get the bug, the amber light keeps blinking indefinitely.

Yes. The display goes into full standby mode when it has received an HDR signal at least once during the power cycle. Just a few seconds in HDR mode is enough for the screen to work as intended.

I have exactly the same problem as well. I just got replacement pg27aqn and it has the same behaviour. The only way I can get the monitor to go standby mode, is to enable HDR in windows. In SDR mode pg27aqn will never enter standby mode. I use my mon...