spatula:
I would say it's a communications error related to the TX of the Leonardo (since you can upload a sketch), but I have no idea of how to test this. Can you just try another Usb cable? Look at the RX/TX LEDS when you connect the Leonardo, then when you upload a sketch, and finally when the sketch is supposed to send data after you open the serial monitor. Do they blink?Another thing you may try is to monitor the Windows COM ports when you upload a sketch. You should see the current COM port disconnect (while the Leo resets), then reconnect (while the bootloader is active), then disconnect and reconnect again (moving to normal operations); maybe the ports are assigned a different number.
The TX light will blink during the sketch upload, but not after that (when it's supposed to be sending the "Hi"). Switching baud rates to 57600 does nothing either.
I did monitor the COM port, and it does go through the disconnect -> connect bootloader -> connect to the original COM port. I am definitely on the right COM port... serial monitor won't open anyway if you're not using an active port.