Just felt I ought to put this out. Had repeated Layout freezing when changing Scenes to Hybrid. Simple model on a decent PC.
Realised I had three copies of an imported ornamental oilive tree which revealed themselves to be typically huge files (Duh)
Deleted and purged the file in SU and now works fine. Will just resort to a 2D tree in Layout and a seperate 3D tree in Enscape. Simple is best!