I will start by saying I have no idea why what follows worked, but I am documenting it here in case I come across the same issue in the future.
We had a model in Revit 2022 where a number of Rooms were not filling the expected plan area. One edge was stopping somewhere in the vicinity of half way to the Wall to which it should have gone; this affected three adjacent rooms, all along the same invisible line. I turned on the visibility of Room Separation Lines (and made them red and fat), but there were none there. I turned on hidden items, I checked the links that were Room Bounding, and I looked at the Design Options that were in the model. None of them appeared to have any contribution to the issue.
I cut some sections to see if there was something on the floor below that could be projecting its influence to the floor above, but that came up empty as well. I knew that there was a setting for Computation Height, and I decided to look into that to see if it was set oddly. It was set to 0'-0" (as I would have expected). To see if there was something right at the Level that was causing the issue, I changed the Computation Height for that Level to 0'-6", and the Rooms expanded to the Wall that was the expected boundary. For grins, I changed the value back to 0'-0", and the Rooms stayed expanded.
That resolved the issue and allowed the project team to get on with their work, but it bothers me that I cannot say why it worked. I get that changing the height forced Revit to recalculate the extents of the Rooms, but why were they wrong at the start? I suppose that will have to remain a mystery, as I have other work to do as well.
