Yes, the pages are built just like stated in Google's article. And next/prev doesn't make sense, as the articles are not related. Canonicals are in place and direct to the category or tag page. The problem is that Google keeps on spidering those pages and signals 404- or 500-errors when there's changes or the server is busy. So we agree, I'll put on a noindex/nofollow on the "load more"-button.
Thanks Dirk!