Thank you for your post.
We recently had an update which appeared to have fixed this issue. Can you please confirm if you're using the latest version of PlusSpec?
If you're not you'll need to download and install the latest version (I've put a link to our downloads page below) then redraw the walls to remove this error. To save you time I would recommend to select all the similar walls (type and height) when redrawing the walls.https://buy.plusspec.com/download
Would you be able to please let me know if this fixes the issue you're having?