I have a strange mesh issue whereby it seems to be transparent when viewed from 1side, but disappears and appears transparent if viewed from the opposite side. To understand this better please view the attached image The shader itself is opaque so I am guessing my mesh is at fault. How can this be fixed?
Check the normals within your mesh in your 3d program. A lot of shaders will cull backfaces, ie. not display triangles that face away from the camera.
You either need to invert the normals for the problem triangles, add extra triangles sharing those vertices facing the other way (effectively creating double-sided triangles for that part of the mesh, useful when you aren’t creating solid geometry and are using a standard opaque shader that culls backfaces), or change your shader to not cull backfaces (probably not what you want, depending on your usage).