Bottom of histogram being cut off

For some reason some of the histograms I am plotting have the very bottom cut off. So the Y-axs goes from 2 - 20 or 10 - 80 or 20 - 140 etc. This only happens on certain plots but causes problem because I am trying to plot several histograms on the same pad which are often quite different in size, so one histogram can almost disapear. Is there a way to force the histogram to display the entire histogram or could there be some mistake in my code?

As you can see from the picture below the bottom of the top histogram is cut off so I can’t see which bins are filled with 0-10 entries. However in the second histogram this is not the case and the code is identical apart from a few cuts.

By default the histograms are drawn from the minimum value, not from zero. Most of the time you do not see this because there is very often a few empty bins. But when you zoom in a part of the histogram where there is no empty bins, you can see that the Y axis does not start anymore from 0. To force the Y axis to start from 0 you can do: