@indxx,
StockChart seems to be working fine with Next.js. Please take a look at this sample project for integration of CanvasJS StockChart with Next.js.
If you are still facing the issue, kindly create sample project reproducing the issue and share it with us over Google-Drive or Onedrive along with sample data so that we can look into your code, run it locally at our end to understand the scenario better and help you out.

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Manoj Mohan
Team CanvasJS