I would like to confirm that this is not a glitch, and feedback shows on the a freelancer's profile after any of the following conditions are met:
@Avery, my work history updates are also unusually slow and I've already met the conditions you listed on two completed jobs. Could you please manually update my profile? Thanks.
Never mind - it's just been updated!
I've been using the fix mentioned by Petra for a while now, after seeing it mentioned by another forum user. It's worked every time for me. I used it yesterday immediately after supplying my feedback (when the client had already supplied theirs). I just added a space character to my overview, deleted it again (without even saving inbetween), refreshed the page, and Bingo!, there was the client's feedback.