I am developing an app with lots of achievements. The order in which achievements are displayed in Game Center is somewhat relevant, for readability reasons. As new versions of the app become available, I'm adding new achievements. Now, the standard approach to change the order of achievements is to drag them around in the iTunes Connect interface, as this answer suggests.
However, as this other question points out, this doesn't always work, and if you try you get a message like "Failed to update sort order. Please try again." (I never succeeded). The mentioned question was closed as off-topic for being a question about "general computing hardware and software".
So, let me rephrase the question from a programming point of view:
I contacted iTunes Connect support about a month ago, since I experienced the same issue with all my apps.
After a 'firewall' answer - which had nothing to do with the problem - they directed me to iOS Developer Tech Support, which is the one you pay and for which you have a few 'free' tickets to spend with your subscription. At this I replied surprised that an apparent glitch in their system would require me to pass through iOS Dev support... so they said "Right, we're investigating the problem and will let you know".
Nothing so far. They answered back to a further inquiry a week ago saying they have no updates on the matter and are still investigating.
Good luck to Sherlock Holmes, then
[UPDATE]
funnily enough, after a month of silence, they fixed it two days after my comment here. Surely a coincidence... ?