Whiskers disappearing on box plots when grouped

Because the treatment is site (a categorical variable) I want to use box plots. I want to show two box plots, one for each site, during six different years. But when I go to group the samples by year the whiskers on the box plots for one of my sites disappear. Is there anyway I can change this so that I have whiskers on both set of box plots?

Would you mind sharing your graph’s URL or a reproducible code snippet (if you’re using an API) ?