Error on exporting Variable Font

On exporting a Variable Font, I got this error:

“Something went wrong while exporting: -[__NSCFNumber hasPrefix:]: unrecognized selector sent to instance 0xa03f1b3c8ac9312f”

Any ideas, what I can do to solve this?

(Glyphs Version 2.6.7 (1356))

Can you send me the file?

Sent to support.

I had a look at your file. The problem is with your names for the TTFStems. As they are sometimes only numbers, Glyphs get confused (I fixed that). But for now (and as you have them only in two of the four masters) add any letter to the name to avoid the problem.

Oh. To be honest, I have no idea, how they get into the masters.

However, it works now. Thank you!