I have a number of Raspberry Pis on my network, powered via PoE. I noticed that some of them would boot back up on their own after having been instructed to shut down, whereas others would remain off as intended - only booting back up when PoE power was cycled from the switch.
I have some Pi4s that are powered by the official PoE+ HAT that all behave properly, and some Pi5s with Waveshare’s G HAT that exhibited mixed behaviour; some would power down as intended, whereas others would reboot after a few seconds.
I narrowed it down to the Pi5’s POWER_OFF_ON_HALT setting, which went set to 1 would cause the Waveshare HATs to reboot the Pi. After resetting the value to be 0 using sudo rpi-eeprom-config --edit, the problem was solved. It’s a shame that the energy consumption will now hover around 1W for these Pis, even when off.