L
Lodger
Most likely a manufacturing fault. As mentioned, If there is clear glass (see through) I can't see how any kind, Quantity or colour of adhesive is going to hide this. The mesh is stuck to the back of mosaic tiles so it's not like the adhesive is going to get between the mosaic and the meshing.
Considering the meshing behind the tile is white, Try and mix some white grout and apply it behind the clear glass mosaic. See if it's less visible!
Considering the meshing behind the tile is white, Try and mix some white grout and apply it behind the clear glass mosaic. See if it's less visible!