The right side cone is covered with a cup style spacer and the cone wrench cannot be used to fully tighten the lock nut. I think this metal cup serves as some kind of seal. How can I retighten cone and nut ?
On quite a few hubs (particularly rear hubs), cone and locknut are only adjustable on one side. The other side is tightened during assembly, before inserting the axle into the hub. If your left side is adjustable, the solution is to undo the left side, take the axle completely out, tighten things on the right, then reassemble and use left side for final adjustment.