I remember this came up briefly on the Facebook group, but I don’t believe it ever made it’s way to the forum. My apologies if I am repeating someone else or if the team is already aware of this.
Under Engraving Options I have Staff labels for identical adjacent solo instruments: set to Group between staves. When setting up Custom condensing groups via Layout Options, the labels still appear between the appropriate staves, except when there’s an odd number of instruments. The leftover instrument always gets it’s own staff label instead of sharing. I don’t know if this is a bug or intended behaviour, but could there be a way for the shared staff labels to appear even when there’s an odd number of instruments?
Attached is a picture demonstrating this. The horns are labelled correctly, but Trumpet 1 and Trombone 7 get their own label instead of sharing. Trombones 1–6 share nicely, but not with 7.