On the attached file. These are objects that have been detached as clones of a larger object. When I click to add a forest lawn to them there is a message saying "To use large areas it's recommended to use Camera > Limit to visibility. Do you want to enable it. Do you want to enable it.
I click yes then nothing appears in the viewport or render.
When I render I get the message: The density of the items has reached the "Max Density" limit.
Only when I attach one of these objects to a plane I create can I get any Forest to show in the viewport and renderer