After the new season (47) started most problems with stale data was resolved but the league endpoint in KR got stuck again and returns stale data (since 2021-04-06).
For example this URL
https://kr.api.blizzard.com/data/sc2/league/47/201/0/5 returns only 3 ladders which is clearly way too few one week into the new season.
I have examples of players that reported this to me as well, the ladders they are in are not appearing in the API. I will not publish their ids due to privacy reasons, DM about this if needed.
Edit 2021-04-16: Now KR ladder data is stale as well.