Coding ligature problems in Glyphs Mini 2

When I export a font with coding ligatures (e.g. => === != etc.) the ligatures stop working correctly. They render correctly, but ‘expand’ to the left and overlap the preceding characters.

Is this most likely due to a limitation of Glyphs Mini 2? If so, are there any work arounds I can try?

In which app are you testing the exported font?

I’ve tried multiple fonts (Fira Code and JetBrains Mono .ttf files) in multiple apps (Visual Studio Code and TextEdit, both on OSX). I have tried simply opening the fonts in Glyphs, and then immediately exporting them without making any changes (other than to the name info so I can install the exported version without conflicts).

Making ligatures for a monospaced font is tricky because of how coding apps force the monospacing. Every glyph is allocated the same amount of space by the app, also a ligature, even though a ligature is representing multiple characters. So you would have to have the same amount of glyphs as before the ligature in order to trick the coding app. The whole point of a ligature though is to reduce the amount of glyphs.

There are workarounds to this (usually done by contextually reinserting the necessary amount of space characters), but it is not possible to achieve this in Glyphs Mini.