Blue lines in Axis toolpath display

Can someone tell me what these horizontal blue lines are or more importantly how to disable or turn them off?

2.9 Deb Stretch Linuxcnc 2.7.14

Thanks,
Kent

If that is a new install then I'd guess an OpenGL issue.
Maybe you could try software rendering.

If it's an old system that did work but now doesn't then i would be looking at hardware issues.