I did watch. When the button is held down what is the voltage reading at D8?

Something like 0.06V when the power supply is 4.8V; 3.3V when 7.2V power supply.

 

That doesn't make sense if the regulator is at 3.3 volts

 

That doesn't make sense if the regulator is at 3.3 volts

I checked it several times. Also,
it seems that the MCU isn't receiving enough power, as the LED on the development board flickers.

 

Are there other regulators as well?
What is the voltage on the output of the regulator using 7.2 volts?

 

Are there other regulators as well?
What is the voltage on the output of the regulator using 7.2 volts?

With 7.2V power supply ams1117 output is 3.47 V. I'll assemble another circuit with LDO regulators in coming days and check what's what. Thanks for your answers!