That's me that must thank you for your immediate reply :) It's not common to receive support within minutes.
Actually, I made it working.
Apparently the bug was in my chart data: I was setting options for the axis (yAxes and yAxisID) with a Chart.js version (2.1.6) that probably didn't not support them yet...I'll try to use a more recent version of chart.js and see if it works.