Greetings Hirokumi,
We believe this is caused because the player has not played since the /achievements/statistics document was added. When new document types/schema revisions are added to the API, characters will need to login and logout before those documents exist for those characters.
It appears that the characters in question has not played since Last-Modified: Fri, 6 Dec 2019 20:14:52 GMT.
Please let us know if this clears up any confusion.