This answer has been locked, yet when I [ask the API about this post][1] it fails to return a locked_date:

[![enter image description here][2]][2]

It's a rather old lock, but I can't see anything suspicious in the timeline or the Post History.

[1]: https://api.stackexchange.com/docs/answers-by-ids#order=desc&sort=activity&ids=31932&filter=!)Q29mbLxf6w2ArlRSR4Kv3ra&site=meta&run=true [2]: https://i.sstatic.net/QAfxo.png