We've resolved this by looking at the network debugger in the browser to see what error was occurring. It turned out we had added the gamecenter entitlement, but hadn't actually checked the checkbox in App Store Connect. Resolved as soon as we did!
JeremyBurgessPikPok
Users receive reputation points by contributing quality content to the forums.
Posts include post and replies published on the forums.
Post authors can mark replies as Accepted to indicate successful solutions.
Apple Developer Forums admins can mark replies as Apple Recommended to indicate an approved solution
Last seen
User for
Post
Replies
Boosts
Views
Activity
Oops - that should say "one of our titles".