The Japanese version of the annual TY email does not include a name in the salutation, and instead is addressing donors as ?? instead of a name.
Zendesk examples are 719403, 719295 (these tickets are from donors who do have both first and surnames in Civi, cid=21269534 and cid=15926654).
Kris noticed similar for Hebrew donors: Zendesk 720832 aka cid=31909717 got a salutation of שלום ??????
Maybe this is an issue with how certain email clients display our emails?