PROBLEM:
The Project Base Point coordinates and/or Elevation have changed in your model file, but no-one has made the change.
CAUSE:
Transfer Project Standards has been used to copy Project Information from one project to another.
Revit copies coordinate information along with project information (Project Name, address, job number etc.)
SOLUTION:
Before using Transfer Project Standards to copy Project Information check the file being copied from has the same Project Base Point values as the file being copied to.
Alternatively create a new dummy project file, transfer Project Information to it, fix the Project Base Point in the dummy file, then transfer from the dummy file to your project.
LESSON:
DON'T trust Revit !