I tried the other emailer (nodebb-plugin-emailer-ssl-smtp) and that works... weird, as I had the local emailer working before, when I had it on my freebsd machine (now centos).
Yeah the calculation doesn't work for subcategories, one reason is we don't have a recursive function to get all children and calculate the counts also we don't have a list of children category ids per category so without adding that this is difficult to achieve.