The UN55 (73x118) I just received has the same issue. The left cup (ID 31.1mm) is quite loose around the shell (OD 30.5mm). There is a shoulder (ID 29.1mm) in that cup that will bear against the chamfer on the end of the shell by some fraction of a mm when both ends are screwed tight. That might be what supports the left side but it does not seem like much.

In my case I will need some spacers (to get my chainline right) so that shoulder will not touch the shell which will then be hanging free supported only by the drive side. I will make a shim to make the left cup fit snugly around the shell.

The UN 52 (73x114) that came out of this particular bike has a plastic cup (ID 30.0mm) that fits without play on the end of the shell (OD 30.0 m).

So the OP and I have an issue and attempting to understand it is not OCD. Those that don't have the problem and don't believe that the problem exists can go ride if they wish. Those with the problem, those who understand the problem and especially those who have a solution to the problem are encouraged to stay here and try to figure it out.