Issue in mesh visualization on HTML5 project

I’m working with UE4 version 4.23.1 and I have noticed some problems visualizing meshes, mostly on the most complex with 70k + faces, as you can see in the pictures.
Has someone already experienced this kind of issue? How can I solve this?

I have also noticed some differences between how the shadow are casted inside the editor and the rendering in the final packed product. Is there some way to see what do you get before packing?

Thanks a lot.

Apparently WebGL has a bottle-neck of 65k vertices for a single mesh.…bgl?