I think I found the cause of this particular error; Glyphs 3 is more discerning with regards to untidy control point placement - so running Paths>Tidy up Paths will likely find and may correct things that didn’t bother Glyphs 2’s “remove overlaps” routines.
So it’s cool that Glyphs 3 has higher standards! If only I could do the same…
Yes, thanks Georg! I’m trying the latest cutting edge. In general it seems the Remove Overlaps is a little bit more exacting - some things which were accepted by G2 upset G3, so I find I’m having to increase the area of overlapping in a few cases… No real problems yet, though!
In florianpircher’s sample file, the problem appears to be connected to the fact that the serif is too wide and “sticks out” of the stem on the right hand side. When I make _corner.serifBottom narrower, the export works. It also works if I decompose all components and corners and run ‘tidy up paths’, which will also remove the zero-width part that sticks out of the stem.
I’m receiving the same error on export with ‘eogonek’.
Looking closely I can see the overlap of the e and ogonekcomb might cause an extra node when removing overlap in some masters due to their paths crossing: