Unicode changes on OTF export

I’m modeling my font on an existing SIL OFL font, and I’ve got the Romans where I like them, but I’m having a problem with the Italics. For some reason, whenever I export as OTF, the unicode of every glyph is decremented by one. I can duplicate this by simply opening the existing italic OTF in Glyphs 3, changing nothing at all, and exporting immediately. “Test” in the original font is rendered as “Sdrs” in the exported font. The unicode tags are correct when I open the original OTF in Glyphs, and typing in the Text Preview window looks and works fine.

Here’s the original OTF.

Here’s the exported OTF from Glyphs 3.

I’m on build 3047.

The problem is that the .notdef glyph has some unicodes assigned. Remove them and also delete the “uni0000” glyph. I already added an error message on export to avoid those confusions.