When using “It” instead of “Italic” in instance names results in a badly built STAT and name table. Could Glyphs maybe recognise this particle as well?
Is that an instance that is just called “It” or is this part of a longer name.
In either case I would suspect that windows is not happy about this.
One instance is called Italic, the rest are called Medium It, SemiBd It, etc.
The reason is that the family has very long names otherwise: Family Sans Rnd Cmp Xlight It is already pushing the character limit.
In places where the length matters, Glyphs will shorten common name particles.
If you use the shortened names you
Also need to pay attention to the style linking (set nameID 1 and 2).
But in general you should rely on the automatic shortening and try to keep the user facing strings full length.
Did you test the unabridged names in Windows 11? I have yet to find issues with variable fonts and had much longer names than this.