I don’t know TablePress, but assuming the script is getting the next page’s worth of posts through an Ajax request that in some way ends up using WP_Query class to get the desired posts, the query could possibly be patched up through the “pre_get_posts” action hook. That’s a lot of assuming though, YMMV.
The request will need to be passing the desired page number or this cannot possibly work. Var dump out the request’s $_REQUEST array to see how the page number is passed. If you can learn how the value is passed, set the “paged” query var with it (if it’s not already correctly set). Also set “posts_per_page” query var to 10 or whatever the correct count should be.
These changes must only be done for the related request. All sorts of queries use this same action hook and you do not want to modify the wrong queries. Usually there’s some unique combination of query vars you could use to verify this is the right query to alter. If the newsletters are a custom post type, that’ll be a good thing to check.
It’d be a lot better if the TablePress script could be corrected. The above solution isn’t ideal, but it’s a possibility if you have trouble getting the script corrected. Even if the query returns the correct newsletters, it’s still possible that the TablePress script will somehow mishandle the data. But at least the correct newsletters are being returned.
