Chartjs-Issue with legend boxes in ChartJS

It could be due to the fact that your canvas isn’t big enough to fit your legend at small enough sizes.

One solution would be to create a custom legend that is completely separate from the canvas. This can be done using the legendcallback function.
e.g

legendCallback: function (chartInstance) {
    //Generate legend here
}

Also, make sure that you have

responsive: true

set in your chart options.

Hope this helps!