Fyi, the following quick settings display the last example fine on my system (just showing edited lines):
using Measures
plot(legendfontsize=6, widen=false, legend=:outerright, size=(1200,600), dpi=600, margins=10mm)
groupedbar!(df.Month, Matrix(df[:,2:end]), bar_position=:stack, lw=0.2, label=permutedims(names(df)[2:end]))
plot!(xrotation=90, tickfontsize=6, xlabel="Month", ylabel="Energy (GWh)", guidefontsize=7)
