I would add to the answer of @JohanC that you must disable "fliers" for the boxplot:

ax = sns.boxplot(data=tips, x="day", y="total_bill", showfliers=False,
                 hue="smoker", hue_order=['Yes', 'No'], boxprops={'alpha': 0.4})

These fliers are duplicates of points already shown with stripplot.