Go to the actual folder
C:\Users\<your name>\Google Drive\
(NOT the Google Drive folder listed under 'FAVOURITES' which is a shortcut).
Right click 'Google Drive' > Security tab > Advanced
Click your username (mine showed <not inherited>)
Click 'Change Permissions'
Check the 'Include inheritable permissions...' box (if it is selected then deselect and select again)
Click ok.
Search indexing of Google Drive should then begin in the background.
