Ah, I see what you mean, I joined the power for the arduino and the LCD together then fed that directly into the 5v pin and the arduino powers on fine but the LCD now shows 4 solid blocks and adjusting the contrast doesn't help only makes them disappear entirely with no backlight.
I feel like I am making a stupid error, I have the wires from the buck converter joined with those that power the lcd then running directly into the pin on the arduino, I read the voltage at that junction at just over 5 but still no luck with the LCD
Update: just tried powering with the USB and got the same result.