Hi, that warn thing is correctly a remnant from the 0.6 → 1.0 release on StatsPlots. I’ve fixed it on master, it’s caused by some irregularity in the code generating the notch size for your data (it’s simply that difference between the 3rd and 4th quartile is so small that there isn’t space to draw a regularly shaped notch. I’ll look at changing the default notch depth). But otherwise, StatsPlots and Plots have been working on 1.0 since 1 day after the 1.0 release.
What happened is that we added dodged (grouped) boxplots to the functionality, but it turns out it broke a rarely used syntax for non-grouped boxplots, which is the one you are using. The ideomatic boxplot syntax, which works and always have worked, is to use a long-format (tidy) format, just like in DataFrames:
tier = [repeat(["Tier 1"], 21); repeat(["Tier 2"], 26); repeat(["Tier 3"], 21)]
boxplot(tier, [a;b;c])
I’d expect Gadfly to expect you to use that syntax as well.
Still, sufficiently many appear to be using wide format plots to StatsPlots and experience errors, so that I’ve decided we need to remove the grouped boxplot functionality again, and look for a different implementation. So I’ve reverted that PR and pushed a new release (v0.10.1).