My Pi4 does not reboot; neither soft nor hard.
It is necessary to let the Pi "cool down" by switching off the supply voltage for at least 3 seconds until it boots again fine.
If powered up immediatly after switching off, the green LED flashes once and nothing more happens.
I tried different images, sd cards etc, same behavior, even without any attached peripherals, without ethernet, monitor and usb devices,. just power supply.
It is 100% reproducable, the required cooldown time varies, but it is never below 3 seconds, sometimes up to 30 seconds (couldn't figure out what causes the variance).
What could cause this behaviour? Which element on the PI has a state when not supplied with power? A capacitor that is discharging? A fuse that is cooling down below a certain temperature threshold?
Edit: The power supply is connected to the mentioned Pi4 and two more Pi3s. Only the PI4 is affected by the problem - it doesn't matter if the other PI3s are running or not - and the PI3s are also not affected and just operate normally if i reboot the PI4 - so I don't think it is the power supply that is responsible for the required cooldown time interval.
Edit2: Voltages are: 3.3v and 4.9v
Edit3: Problem persists even without any SD Card: The green LED flashes to indicate that no SD Card was found only after waiting for the required time, otherwise it just flashes once.