Mesh3D folds the surface when shifting along one axis

Hi there,

I have two meshes and I merged them into one mesh3d plot. It works however I also want to shift one mesh a certain distance along any axis. What I don’t understand is when I shift too much, both surfaces will be folded. Here is the code,

p <- plot_ly(
    x = c(surfL$vertices[, 1], surfR$vertices[, 1]),
    y = c(surfL$vertices[, 2], 
          surfR$vertices[, 2]),
    z = c(surfL$vertices[, 3] + dist, surfR$vertices[, 3]),
    i = c(surfL$faces[, 1], dim(surfL$vertices)[1] + 
            surfR$faces[, 1]),
    j = c(surfL$faces[, 2], dim(surfL$vertices)[1] + 
            surfR$faces[, 2]),
    k = c(surfL$faces[, 3], dim(surfL$vertices)[1] + 
            surfR$faces[, 3]),
    type = "mesh3d",
    vertexcolor = col

When I set dist small enough, it plots what I want, for instance, dist = 100 plots like this,

Then dist = 200 plots like this,

However, when dis = 300, I got folded meshes

I also tried on x and y axis, it seems as long as the range of one coordinate is larger than 500, it will wrap the surface. Could you please help to figure out why? Thanks a lot.