Facebook API doesn't return message_tags with app token

I am trying to get user mentions (message_tags) included in comments. I am making this request from Facebook explorer:

GET / v2.10 / 1575295176130351_1877507262575806? fields = comments {message_tags}

When I'm authenticated as an app with an app token: Facebook API only returns message_tags of type 'page'. The API does not return message_tags of type "user".

When I am authenticated as a user, with a user access token: it returns all message_tags.

Can anyone explain the reason for me? I was able to get message_tags from type "user" with application token 2 weeks ago ... I suspect the API has been updated, but I cannot find any clear explanation in the change log.