I finished this font in Glyphs 2, did a final run-through in Glyphs 3, and now I get this message when I export as both .otf and .ttf. Keep in mind, they did export in Glyphs 2, but not anymore. Any help would be greatly appreciated.
The default for compatibility checking has changed. To get the old behavior back, add a ‘Enforce compatibility check’ custom parameter in the font settings and deactivate it.
If you not “enforce” it, Glyphs will look into the instances and check if there is any interpolation going on and will check compatibility only between actually interpolating masters.
I stumbled upon the same problem. But the solution you recommended does not work for me. Also, quite a lot of weird things happened all of the sudden. Now when I export my font in OTF it mixes masters or does not export them at all.
Attaching a screenshot of stems exporting with different widths etc. One is from glyphs, where the stems are closer width and the other one is from illustrator. Quite a noticeable difference. Weird stuff happening. (not sure if this thread is the right one, but it seems like it started with the same issue.