Why is my NAND not working with a load attached to it?
The logic gates must have low output impedance and high input impedance, otherwise the logic circuit formed by connecting these gates will not work properly, also each of them, as a standalone circuit, may function as desired because the oscilloscopes or the multimeters have high input impedances.
In other words if the the second gate draws a lot of current from the output of the first, both circuits will malfunction.