I don't have enough reps to comment. But clearing the cache did not work for me. Using the main CDN also generates Highcharts undefined. Using this: <script src="https://code.highcharts.com/highstock.js"></script> instead of <script src="https://code.highcharts.com/stock/12.1.1/highstock.js"></script> breaks the above fiddle. This chart runs on the website but not in the fiddle. There is also a similar situation with Highmaps.