The grid pattern exhibited in the STL exports is inherent to the process Equator uses to generate them. In order to generate the STL, Equator first process the source LiDAR into a raster elevation model. This raster product stores elevation data in a pixel grid, much like a digital photograph stores colour information in a pixel grid. This pixel grid is the source of the grid pattern you are seeing. By lowering the pixel resolution value when you perform your export (e.g. 1 pixel edge is 30 metres long -> 1 pixel edge is 1 metre long), this grid is made finer. In this way, you may be able to reduce how noticeable the grid pattern is in your final product.