FeatureLibError: Expected a glyph class with X elements after "by", but found a glyph class with Y elements

Compilation of the following sources failed.
All of these sources were created by importing a TTF file into glyphs.app and saving it as a GLYPHS file.

Bug in glyphs.app? Bug in pipeline?

[gNotoSansBatak.glyphs.zip](https://github.com/googlei18n/fontmake/files/622117/gNotoSansBatak.glyphs.zip)
fontTools.feaLib.error.FeatureLibError: instance_ufo/NotoSansBatak-Regular.ufo/features.fea:6:1: Expected a glyph class with 1 elements after "by", but found a glyph class with 2 elements
[NotoSansBatak-Regular.ufo.zip](https://github.com/googlei18n/fontmake/files/622196/NotoSansBatak-Regular.ufo.zip)

[gNotoSansSyriacEastern.glyphs.zip](https://github.com/googlei18n/fontmake/files/622119/gNotoSansSyriacEastern.glyphs.zip)
fontTools.feaLib.error.FeatureLibError: instance_ufo/NotoSansSyriacEastern-Regular.ufo/features.fea:386:1: Expected a glyph class with 160 elements after "by", but found a glyph class with 480 elements
[NotoSansSyriacEastern-Regular.ufo.zip](https://github.com/googlei18n/fontmake/files/622197/NotoSansSyriacEastern-Regular.ufo.zip)

[gNotoSansSyriacEstrangela.glyphs.zip](https://github.com/googlei18n/fontmake/files/622120/gNotoSansSyriacEstrangela.glyphs.zip)
fontTools.feaLib.error.FeatureLibError: instance_ufo/NotoSansSyriacEstrangela-Regular.ufo/features.fea:239:1: Expected a glyph class with 153 elements after "by", but found a glyph class with 405 elements
[NotoSansSyriacEstrangela-Regular.ufo.zip](https://github.com/googlei18n/fontmake/files/622198/NotoSansSyriacEstrangela-Regular.ufo.zip)

[gNotoSansSyriacWestern.glyphs.zip](https://github.com/googlei18n/fontmake/files/622121/gNotoSansSyriacWestern.glyphs.zip)
fontTools.feaLib.error.FeatureLibError: instance_ufo/NotoSansSyriacWestern-Regular.ufo/features.fea:412:1: Expected a glyph class with 156 elements after "by", but found a glyph class with 483 elements
[NotoSansSyriacWestern-Regular.ufo.zip](https://github.com/googlei18n/fontmake/files/622201/NotoSansSyriacWestern-Regular.ufo.zip)