I then began to determine that it was the text in the drawing that created the faults.
A lot of my files originate from V14 or earlier TC versions...
I now mainly use V21.
The Text can give strange results when i use V21 to modify files from earlier versions.(This is not confined to a V21 issue, as i have other versions)
Solution is to just Create a Blank new file.
Select all / Copy n paste via the menu (not via RH click of mouse) from old file to new file.
Recreate your viewports and paperspace.
The New File
should now be stable and good to go.