It’s rare that I use groups, but I do have a doc with a dozen variations on a layout in a frame that I had grouped to hide the frame names on the canvas and I was surprised that when I selected a child frame in one of them, Select Matching Layers returned “No matching layers to select” for what should have been matches for the other child frames of the frames in the group (and do match if those parent frames are ungrouped).

I would expect Select Matching Layers to work the same way in a group as it does for a section (where matching children are found, but limited to within just the parents in the section). I guess I’ve always considered the contents of groups (and sections) to be a “loose” collection compared to the “rigid” collection of the contents of frames.