Or is this tied to the difficulty and if you play on Very Hard or Survival it skips the screen where you can choose 2 traits (after you distribute the 21 attribute points)?

Had this happen too, and judging from the first minutes of a couple playthroughs it certainly is not just a few instances. Some got to the traits selection and choose while for others it was skipped entirely.

Maybe another fresh install from the offline installers of both FO4 and Fallout: London might help solve it?

Same here. It worked on my first playthrough but after a fresh install it's not appearing.