This means our review team has not come to a clear decision during the initial review, so we’re putting extra effort and resources into reviewing your channel multiple times before making a final decision. Hope you hear back soon.
While we can't get into specifics, when we review your application we look at your channel activity–things like uploaded videos, strikes, views, subs, and watch time. Keep uploading original/public content as the more info to review, the better. Hope this clarifies.