No, the issue is not obvious. I see nothing wrong at quick glance when I run your script. But if a plot does not look right, follow first the bug fixing instructions in the manual. In your case, that would be printing the plot values in the log and checking them against the plot, by zooming at a certain date if needed. If you cannot fix it this way, the final solution is getting a support ticket and asking my colleagues for help. That will always work.

If you contact support and it turns out that the issue is caused by something amiss in the manual or by a Zorro bug, we refund the support ticket of course. But I must tell that this does not happen often.