Glyph won't interpolate

I’m trying to interpolate an ‘f’ between two extremes. If I place the exact same outlines in the ‘one’ position both extremes interpolate, but when on the ‘f’ position they don’t. Nothing blends in the ‘f’ position, even similar circles. Why would this happen?

Can you post the outlines of extremes?
Something like this sample.

Sure, here they are, exactly the same nodes and starting points:

Then the layers probably have a different shape order. Fix that with Command-Option-Shift-R or with the Shape Order dialog: FilterShape Order.

They’re the same.

Maybe there is an issue that is caused by the serif components. Otherwise, can you send us the file (or just the glyph)?

The corner components were the problem. They work fine in all other glyphs.

Best to select one master and run the Propagate Corner Components script in the mekkablue scripts.

Thanks, that worked.