For whom anyone found here for similar problem, I solved this with frustumCulled option as false on every child objects of model with the code below.

model.traverse(node => {
  if (node.isMesh) {
    node.frustumCulled = false;
  }
})

FYI, frustum culled means that the model, or the part of the model which is not showing the frustum-which means the viewport of user inside the scene-is visible or not.

image reference: https://bruop.github.io/frustum_culling/