Some glyphs don't interpolate in variable font

I’m working on a variable font with one custom axis that I’ve named Flex (FLEX). The two masters change the shape of the ends of strokes. one is cupped (concave) and one is rounded (convex). I’ve been testing as I go along and there’s some glyphs that won’t interpolate at all in Illustrator CC (v.22.0.1) even though the masters are perfectly compatable. Most of the glyphs work fine but there are seemingly random letters that stay stuck on the first master when dragging the Flex axis slider. The font works perfectly in both FontView and Axis-Praxis so perhaps this is an Illustrator bug?
Any suggestions?

I’m having a similar problem, however some glyphs won’t interpolate even on Axis-Praxis.

I’ve generated a .ttx and noticed the affected glyphs don’t have glyphVariations tags in the gvar table. All drawings are compatible inside Glyphs.

This is how it looks on Axis-Praxis:

Do you have instances defined that interpolate on all axis. That would trigger a compatibility warning. Or add a Enforce Compatibility Check custom parameter to the font.

No change for me. I have a single axis. All glyphs interpolate fine within Glyphs:


Should I send the file to support?

Adding Enforce Compatibility didn’t make any changes for me.
I did notice there was a glyph that had no start point at all on a contour. Or at least it wasn’t indicated with an arrow. Once I fixed that with correct path dirrection, the glyph interpolated correctly.
But there are still glyphs that seem perfectly compatable that don’t interpolate.
I beleive my masters/instances are set up properly.
can I send you the file?

Can you send me the .glyphs files please, to support (at) (this domain). I will have a look.

I’ve just figured it out my issue: I was exporting the fonts with the Don’t use production names custom parameter. The glyphs that were not interpolating are the ones that would be automatically renamed on export:


I’ll send you the .glyphs file in case you want to have a look.

Please send the file.

@GeorgSeifert I have the same problem with my created Variable font (one axis, width). On webtools like font gauntlet or wakamaifondue every single letter has a smooth interpolation, but it’s not working in illustrator and photoshop. A few letters are stuck. Did you solve the problem, and how did you do it?

FYI, @Steff contacted me for help as well and I took a look at the file. What I found is that the variable font exported from Glyphs do not work correctly in Adobe apps, but the variable font generated with fontmake from the same .glyphs file do.

I do not have sufficient knowledge to tell what’s wrong with the generated ttf file, so maybe @GeorgSeifert or @mekkablue can help.