@Wolfgang Thanks for that, I had done several uninstalls but using an uninstal file in 'Programs/DXO/Nik Collection/… which I think may have been a left over from a previous installation(?)… Did a ‘proper’ uninstall via ‘Settings/Apps’ and it seems to have done the trick. 
Now I just need to find out why Color Efex crashes with more than one image loaded whilst swapping recipes?! 