I have two masters - Light and Bold. All the paths are correct, without any errors. I create instances - Light, Regular, Medium and Bold. I export my fonts as otf files, so I now have four fonts. I am submitting them into MyFonts and the system reject my fonts because there are errors with the paths in each of my fonts. I again open my exported fonts in Glyphs program and I can see that there are errors with the paths, even though my initial masters still don’t have any errors. What am I doing wrong??
Can you post some screenshots?
This are most likely kinks. That happens when three or more collinear points have different angles and proportions in the masters.
Kinks are explained explained in the Multiple Master tutorials: https://glyphsapp.com/tutorials/multiple-masters-part-2-keeping-your-outlines-compatible
For tracking kinks, see the Kink Finder in the mekkablue scripts and Henrique Beier’s Show Smooth Node Angle and Proportions plug-in (available vie Window > Plug-in Manager).
You can avoid the inflection if you delete the handles on the thick stem and turn that segment into a straight line. As far as i can see, all the handles are collinear and describe a straight line.
The hinting settings seem to be not ideal either. I recommend this tutorial: https://glyphsapp.com/tutorials/hinting-postscript-autohinting
Or actually, this high contrast design can probably better do without hinting altogether.