Ok so i think i have solved my problem, it seems like there was some form of Bug in the 'Start up Scene' that is created when loading Terra for the first time, because of this issue, every save i made after startup included the issue, and so every scene created there after was corrupt.
Solution - Opening one of the sample scenes 'Canyon' and stripping out all of the Canyon create nodes except the compute terrain node. (Keeping the rest of the scene in tact).
Then saving this as my new 'Start up Scene' ... i realised you can set a default startup scene in the preferences... so now i have a clean working base to work from.
Fun times....but nothing surprises me in 2020. :-)
Thanks for your time
@duke though... your idea of deleting the phantom Camera one is what got my tiny brain ticking.
:-)
JK