I'm having the same issue that was reported earlier in this thread regarding Premium Economy results not being displayed.
Here's what I see
when logged into my 1K account:
As an experiment, I tried
logging out of my account, and then it worked properly:
As a 1K member, united.com doesn't seem to want to sell me Premium Economy tickets!
Note: I've tried this experiment in two different browsers, and I've tried clearing my cache and cookies, but the problem persists.