Lines dissapearing when click or release mouse

I have been on this file among others to improve my SU. I have had the 5 files saved as I go I am now at version 31 with
the building
the landscape
the road applied to the land
so now I progressed to plan landscaping with a pond
and wanted to set the road on the landscaping layout to delete
unnecessary lines crossing from the landscaping across the access and exit road
Before this I had the (above right layout) on the left of the building
so I moved it to the right just to be closer to the road layout and copy it over
SINCE THEN every time I click on the landscaping file
when I click on the mouse the mosaic pattern disappears
when I release it it appears again.
I tried to ignore it and exploded both and set them into one file
set the road on the same level as the landscaping
BUT I ended up seeing the road but NOT the landscape pattern
to do what I had planned delete the lines over crossing each other
as I want to project it after in position around the building
so I can plant

and fictive put rocks and patterns of stones etc…for a possible rendering