Live and learn -- lol. That's part of why I am doing this project, to learn something new.
Thanks for the info. Using the 3.3 volt rail unless something requires 5V like the LCD display backlight.
John
I'm guessing that the strange behaviour you are seeing is because there is a forward diode connection between the GPIO pins - the internal protection of the controller.
If you had given proper measurements we would have seen the connection. "5V" and "4V" is not sufficiently precise.
Does your DMM not provide ANY decimal places? 5.0x and 4.3x would have been more useful.
That's a great motivation and probably the reason for a majority of people here in the forum!
Just be careful when you dive into a project that handles mains voltage... One wrong move might stop the learning curve immediately 
Have fun with Arduino!
ec2021
recommend you avoid peripheral devices and sensors which use 5V logic
some devices may use 5V as the power input but the interface uses 3.3V logic, e.g. TFT displays - refer to datasheets
a useful general reference is esp32-pinout-reference-gpios but also refer to the pinout for your specific ESP32 module