Hi Irene,
Do you use a MouseTracker element both for the clicks on the Canvas at the beginning of the experiment, and for the selections on the test trials? You can share your experiment with me by sending its URL at support@pcibex.net if you want
Did you make sure that the content of your experiment fits entirely on a 360×720 screen, and that your participants don’t need to scroll down to make a selection at the bottom of the page?
Jeremy