I have imported over 1000 articles from one version of tt_news (2.5.2) to the latest version, I also imported the news categories. Everything seemed to come across except the news categories don't appear to be assigned to the articles if you view them in list > news articles folder, but they do appear when you go into the table in the database. eg the article with uid = 1 has category 2 assigned to it in the tt_news table but when you view it in list > news articles it says has no categories assigned. Is there some bulk action I can use here to get all the categories assigned?
category column in the tt_news table signifies the number of categories assigned to the news article while the relations between news and categories is in the tt_news_cat_mm table.
Therefore, check the tt_news_cat_mm table and see whether the relations are truly there as they are supposed to. The uid_local column contains UIDs of the news articles while the uid_foreign column contains UIDs of the news categories.