Hi,
Note that this mass action will only delete up to 10 (due to the "10" in the value field of the limitations section of your mass action) unpublished products each month.
If each month, you unpublish more than 10 products, then the unpublished products will start piling up.
Similarly, if you manually process the mass action, it will only delete up to 10 unpublished products. If you have hundreds of unpublished products, you might not notice that 10 of them have been deleted after the processing of the mass action.
On top of this, note that the mass action on the "product" type actually process both products and variants. So if you unpublish 100 variants of a product, then for just that product's variants to be processed by the mass action will require 10 months.
Because of all of this, I'm thinking that the mass action is actually working, but you just don't notice it because it's not processing enough products / variants often enough.
Also, you want to check that your cron task is running :
www.hikashop.com/support/documentation/5...cron-task.html#check
If the cron task is not running, then the mass action won't be called every month.