'U' will not interplate


I’ve been very busy working on a font with two Masters, the ‘U’ glyph will not interpolate. All the others are working fine.
I’ve tried out all the possibilities in the Glyphs Handbook (chapter 10.5, page 80), but nothing works.
Georg thought it might be missing Anchors, but this is not the problem. Other glyphs have missing Anchors and they work just fine. I have the right Anchors in both Masters, but… nothing.

Did anyone have this too? Perhaps any thoughts on a solution?

Sometimes when I select the point and move it I have to move them with Alt pressed not to move handles.
And sometimes I press Alt to quick and it duplicate point. It is not easy to figure out an plain point but check your second master, if there’s a fourth starting point maybe.

If not, try to remove overlap and see if it works. You can always cut steams back.

The outlines are green, so the glyphs in both Masters are compatible. This means that there can’t be an extra point.
But to be sure, I checked it again. Still green but… removing the overlap did the trick. I’ll keep a copy in the background, in case I need to change the glyph in the future. Must have been a corrupt outline.

Thanks for the tip.

The pic doesn’t open for me.

(In Glyphs 2, the anchors must be in sync too, otherwise it won’t interpolate. There’s a script in my github rep to sync anchors.)

Perhaps select all and look how many nodes there are (indicated in the grey info box). Maybe there is a doubled node, or a node out of bounds.

Removing overlaps also removes stray points and open paths, so I guess that must have been it.

This was indeed an corrupted outline.