@sepetar,
From the CanvasJS v1.8 to CanvasJS v2.3.1 we have added many new features to the library because of which the performance may vary by only a few milliseconds.
However, if you can create a JSFiddle reproducing the issue you are facing and share it with us we will look into the code, understand the scenario better and help you out.
____
Shashi Ranjan
Team CanvasJS