Highcharts does not resize charts inside tabs-Collection of common programming errors
This is my fix for this (using jQuery):
$.each($("[data-highcharts-chart]"), function () {
var highChart = Highcharts.charts[$(this).data('highchartsChart')];
var highChartCont = $(highChart.container).parent();
highChart.setSize(highChartCont.width(), highChartCont.height());
highChart.hasUserSize = undefined;
});
Call this function whenever the chart gains focus to make sure it is resized properly.