I think this has something to do with the recent change regarding close reasons.
Some of the reasons have gone (unintentionally?) missing:
On Super User, I no longer see the "no longer relevant" reason.
And on Meta, there are even only three left, namely "dupe", "not SO related" and "too localized". Where are the others?
Side effect is that questions closed with a now gone reason have no reason at all.
Case in point: a question previously closed as "no longer relevant" doesn't display any reason at all (yes, it was a bogus reason to stop the many spam answers that should now be fixed):
Edit: Reverted this back to [bug] as the "empty close reason" is still an issue that needs to be fixed.