The sorting is not working as expected since a few hours.
Can be tried in the API explorer (Execute without OAuth) as well.
date: Resources are sorted in reverse chronological order based on the date they were created.
https://developers.google.com/youtube/v3/docs/search/list
What is going wrong?
In case you are looking to get the latest videos of a channel:
Alternatively, you can use the channels RSS feed:
https://www.youtube.com/feeds/videos.xml?channel_id={ChannelId}
https://www.youtube.com/feeds/videos.xml?user={User}
This does not replace the full search sorted by date function however.
Thanks YouTube for making me work on a Sunday, all I wanted was to watch the latest videos from my favorite channels. At least I don't have to wait for a fix anymore, good luck to those less lucky!