Posted this in GPU tracker thread but will do so here, too. Just like many of you, I am also looking my reservation like a hawk and noticed

! A modification has been made to your itinerary. Please contact United Reservations to have your ticket reissued.

Given the message, I started looking into whether I could pick a biz class seat on any uncleared segments and, what do you know, I was able to get into NRT - SIN UD but there was nothing to lead me to decipher that (besides the comments on this forum).