Kerning export failure?

I’ve been experiencing weird behaviour in kerning (build 679). The font that I could export gives kerning overflow error now (even with useExtensionKerning active) and requires a lot of optimisation, which in the end I could export. But even after that, I notice that some pairs don’t end up in the font whereas they did in earlier versions. What’s going on? What did you change?

Above: Pairs missing in my font, exported with build 679
Below: Same font, exported with an earlier version (intended result)

[added] I also compared font files generated from (almost) the samefile but different Glyphs versions and the final font file size differs by 30—60kb. For example, the one with all kerning pairs is 289KB but the newest one with less pair (that gave me a lot of overflow errors) is 329—354KB, depending on how much I optimise kerning groups. I think that the OpenType code generator in the new build has become inefficient.

can you send me the .glyphs file? I changed the kerning code quite a bit and it might need more testing.