Welcome to our forum & thanks for the question!
In this demo, everything seems to work fine: https://jsfiddle.net/BlackLabel/xLqpvye4/
Could you please try to reproduce this in an online code editor like JSFiddle so I can take a look?
It's worth keeping in mind that there are different settings for column.stacking
as explained in the API - https://api.highcharts.com/highcharts/s ... n.stacking
Depending on which one you use, your columns will be stacked based on a different method.
Please let me know if that helps.