I'm wondering if this has been resolved before.
If you create a graph inside a hidden tab, the labels are not displayed properly.
I think this is an issue with native getBBox() method where in hidden elements does not return correct bounding box data.
I have recreated the issue in jsfiddle,
here:
Also, if there is a fix, can you let me know or how can I contribute to your code.
Regards,
Marco