See https://discourse.hibernate.org/t/indexation-post-treatment/3753/12?u=yrodiere

The problem is that, when the indexing of multiple entities failed, we give up on reporting all failing entities when even just one document ID cannot be converted back to an entity ID, but all other document IDs can.

Ideally we'd just log the failure to convert the document ID somewhere, and still report the other entity IDs.