When attempting to drill-down from Canada into the province of Newfoundland and Labrador the hc-key is up-to-date with the latest provincial code as "ca-nl", however, the code.highcharts.com/mapdata API is outdated and is still using the old provincial code "ca-nf". I have found a workaround, but I figured you should be notified.
So basically the API endpoint should be changed to code.highcharts.com/mapdata/countries/ca/ca-nl-all.geo.json instead of code.highcharts.com/mapdata/countries/ca/ca-nf-all.geo.json
When attempting to drill-down from Canada into the province of Newfoundland and Labrador the hc-key is up-to-date with the latest provincial code as "ca-nl", however, the code.highcharts.com/mapdata API is outdated and is still using the old provincial code "ca-nf". I have found a workaround, but I figured you should be notified.
So basically the API endpoint should be changed to code.highcharts.com/mapdata/countries/ca/ca-nl-all.geo.json instead of code.highcharts.com/mapdata/countries/ca/ca-nf-all.geo.json
Here is my example code with the workaround: https://codesandbox.io/s/canada-basic-nl-issue-eeezj?file=/demo.jsx