See the images and video below.
I decided to do some digging, and after opening the CAD file for some exploration, I soon realised the Grid lines were an X-Ref that had been bound into the drawing, but not exploded. Once I exploded the bound X-Ref, and re-loaded the linked CAD file, the grid lines once again lined up perfectly.
See image and video below.
This problem is encountered with bound X-Ref’s that are not exploded, and also with any nested blocks that are not exploded. I also noted that when trying to rotate an object, Revit struggles to snap to the intersection of 2 lines in a linked CAD file that are either unexploded X-Ref’s or blocks.