Hey ,
With the way you have your mesh set up all on one model, and the at which you are viewing the wooden walkway the flickering will always be there. The ‘flickering’ you are seeing is actually something that also happens in real life if you are viewing a collection of objects that are parallel and close to one another and viewed at an angle. Another term for this is called the ‘screen door’ effect or the moire pattern. Documentation on this effect can be found following the link below, which will go into great detail about the ‘Moire’ pattern.
Moire Pattern
This effect can be reduced by changing the approach you are using when modeling your mesh. The first point of interest would be to edit the UV map of the mesh. Having a clean unwrap when modeling can make a world of difference when using lightmaps and baked lighting. If you need help on how to improve your Unwraps or your Static Meshes follow the documentation provided below.
Static Mesh Pipeline
Unwrapping UVs for Lightmaps
As I mentioned before, you could completely avoid having to do this if you simply modeled out a single 2x4 piece of wood to use as your walkway piece and applied that to a new ground mesh/plane.
Another approach you could take, which would save you polygons and reduce the visual flickering your are seeing, would be to create the walkway pieces as a normal map. This way you still get the small amount of raised detail from the normal and you avoid creating geometry entirely.
The final contributing factor to the flickering is the Anti-Aliasing. You can turn this setting off within your ‘Post Process Volume’, which should reduce the flickering, but the edges of your objects will appear more jagged. If you have any other questions or need help let me know.
Cheers,