Hi,
I’ve discussed this with some colleagues who have noticed the same warning. Apparently this warning can appear if the scene has lots of shadow casting lights or contains a (shadow casting) particle system, even if there are few non-Nanite meshes.
Just to confirm, do you want to see a list of offending (non-Nanite) meshes when the warning is displayed? That is currently not implemented, but I can potentially pass this as a feature request to Epic.
One way to list Nanite and non-Nanite meshes is via the Property Matrix (in the Outliner, bulk select all meshes, right-click and choose “Edit selection in property matrix”, press the pin next to Nanite>Enable Nanite, in the content browser you can do the same by right-clicking a selection and choosing Asset Actions).
Best,
Sam