Group Strikethrough

Hi, am quite new to Gannts in general, and just getting used to scheduling, etc. One thing I can’t quite work out is why sometimes groups of tasks scheduled for the future have their title with a strikethrough text, and sometimes they don’t. I think it happens because they can’t start yet (if dependent on proceeding task/group) - but I can’t find any information here or in the manual. Can any kind soul explain?