Ok, I'll give you an example of this behavior.
If you look the source from this category page http://www.parafarmacia.it/benessere (SmartSEO is active with 'Append product names to keywords for category pages' on) you'll see the keywords with the name of the products on the page: ok right. Now go to the second page (or click http://www.parafarmacia.it/benessere#/pageSize=18&orderBy=0&pageNumber=2) and look at the keywords of this page: you'll see the same keywords of the first page, not the name of the products on the second page. And so on. Thank you.
Sorry for the late reply!
Please note that you have the Ajax Filters enabled and the second page is open via Ajax, which means that the page is not refreshed and you are basically on the same page but only the products are different. Please note that the search engines simply ignore anything that is after the # tag in the URL.
So the SEO Meta Data would change only after you go to the second page without Ajax i.e yourstore.com/category?pageNumber=2.
Actually there was a caching issue and the Meta Data was cached the first time you visit a category for example and it wouldn't change if you visit the other pages. We fixed this issue and now each page shows the correct Meta Data. You can update the plugin as explained here