Can't share my solution and can't view others

I've solved it already. But trying to view someone else’s solution I’m told “If you want to see solutions of other users you need to solve this mission first”.

And the “Best Solutions” link is greyed out and tapping it brings up the message “There is no ability to publish solutions for this task”.

And indeed when I try to share mine, I get a red "not publishable" error bar.