Hi,
Thank you for contacting us with your issue.
This is indeed a very interesting problem. From what I can see, in your case it's mainly due to
pointPlacement: 'on'. However, if instead of defining the start navigator's range with
range instead of
min and
max for the axis, everything should work fine.
Check out this demo:
https://jsfiddle.net/BlackLabel/aymofr7p/
If you think it should be reported as a bug, do so here:
https://github.com/highcharts/highchart ... new/choose
If you have further inquiries, you may reach out to me at any time.
Best regards!