@David,

I do a lot of reviews, and I've only had this problem once. Must mean the database is up to date. No soft reset necessary; after X'ing the popup and reloading the lesson page everything was fine.

It is helps, the culprit was 康师傅 from the Elementary "A Betrayal of Family" lesson :-) I've added the word to my private word list and will see it comes up again.