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It was my mistake, I was passing the data with a wrong format.
In codepen code above, X and Y data were passed using two different array (the first as labels). I should have passed the XY data as a single, two components array.
There is another codepen in my dashboard (Chart.js Linear Zoom example) that shows the way to beginners like me 🙂
Callback for ticks was definitely not the problem.
Source:stackexchange.com