I know there are higher priority fixes at the moment, but I could not manage to find the game of the week function on the completed games page. I wanted to vote for Diduk-Lubuna.

That game was certainly a worthy choice! This feature is unavailable for the same reason that it is not possible to view completed games via the pairings page or completed games page - they direct to the wrong link. This can and will be fixed retrospectively, but unfortunately there are more pressing problems...