I had a solid group that needed to contract a little bit, so I did a subtract to cut out the extra, made the two halves into groups, then I moved them together (closing up the gap), then did a union to join the two groups. This worked fine and now I have a complete shape which is correct
However, Sketchup does not recognize the resulting shape as a solid group anymore. It considers it a "difference" with a sub object which is a "union" (see image below). How can I turn the object into a ordinary solid group?