Ugly diagonal strokes in interpolated variable font

Hey everybody.
So @GeorgSeifert I tried this little “intermediate” layer trick, and it helped me a lot !
I use it with all my characters with diagonal strokes (A, K, M, …) and it works really fine, except for some of them who strangely behave when I use the axis slider. Here is an example in illustrator (the problem is the same in InDesign or Photoshop)

I stretch the font from 200 to 1000 on the width axis. Please look at the “2” number. As you can see, it doesn’t change until 600, and then it starts growing…
I don’t undesrtand why this is happening with this glyph : does someone knows what is going on here ?