We have been using grading for years to tie fill & cut feature lines back into the existing ground surface. Mostly use grade to surface. No major issues through the years.

Now we have a model file with Finish Grade surface and Existing Ground surface. The file is pretty big (12 MB) because it is a big project.

We have not worked in the model file for a couple of weeks. When we got back in the file to modify the grading, all the grading objects have converted (exploded?) into feature lines with multiple vertices.

When we create a new Grading with Grade to Surface, the new grading immediately converts to feature lines with multiple vertices. It does not exist as a grading object.

Any idea what is causing this and how to fix it?

Thank you in advance for your help.
Arthur Spencer