Is it possible to interpolate static/variable fonts from a GlyphsApp source with incompatible Roman & Italic masters?

I am working on a font in GlyphsApp, and it has incompatible Roman & Italic styles.

This is (mostly) pretty convenient, as most of the info is shared between roman & italic fonts, but the lowercase is mostly incompatible across the ital axis. This generates as expected when exporting static fonts directly from GlyphsApp, but I keep hitting interpolation errors in FontMake:

```
fontmake: Error: In 'source/name_mono-wght_400_900-ital_0_1.glyphspackage' -> 'master_ufo/ATNameMono231016.designspace': Interpolating instance 'Medium' failed.: Failed to generate instance of glyph 'a.italic': list index out of range. (Note: the most common cause for an error here is that the glyph outlines are not point-for-point compatible or have the same starting point or are in the same order in all masters.)
```

I’ve gone through and made sure that all such glyphs (`a.italic` in the above example) are compatible within their side of the ital range.

Do I have to split up the sources into two separate Glyphs sources, or go to UFOs via FontMake, before then building the binaries?

Just hoping to know what to expect. Sorry if this info is already kicking around somewhere... I couldn’t find it so far.

Thanks for any pointers!