Hi there.
The mentioned landscape layer probably doesn’t have any LayerInfoObject associated.
If you used UEFN to create the landscape, these should be automatically created, but maybe they were not saved so don’t exist anymore. Make sure they are always saved in the future to avoid this type of issue.
You can still fix this issue by either assigning an existing LayerInfoObject to your layer (left arrow in the screenshot), or by creating a new one (right arrow, the “+” sign, make sure to right click and save the asset once created).
Hope this helps