I dont think you’ll ever get anywhere with this.
Even if fully instanced you are dealing with a massive amount of meshes for something as simple as a road.
Further, because its linked to a spline the mesh instances are all custom deformed making it impossible to instance.
The proper way to do this is to generate the mesh on the fly.
Not to generate a road out of pre-cut mesh parts.
You can “parse” a pre-cut mesh part to mimic its final shape, read the vertex and transfer it over to the final mesh component.
Being you are just using a spawner it’s not going to do that for you(op) or work.
And @Nebukam its totally possible, it’s partly what is supposed to happen.
There is a ton of new content on this.
You are looking for acrual mesh generation, Not mesh placement.
Mesh placement will almost never work with splines in normal like environment scenarios.