Hi,
I work in Glyphs 2.6.8 (1361) and found the difference in generated variable TTF files containing bracket layers. If custom parameter [Feature for Feature Variations _ rlig] added to the Font tab, then substitution to shapes containing in bracket layers works fine in Web (fontgauntlet.com) and InDesign 2021 (build 16.4). But without the custom parameter bracket layers in TTF don’t work in same apps. It’s strange because in first and second cases Glyphs generates RLIG feature.
Another problem is that CPSP feature not working with RLIG. Capital spacing activated for basic letters in @Uppercase class, but I can’t find the way to make it active in alternates activated with RLIG (glyphs containing with bracket layers). Maybe you know the trick?