@Hugo
If you do not use page ID, Osclass is still able to identify static page based on slug.
However it's not possible to use just page slug without anything else. It's not possible to differentiate if you are talking about static page, category page or home page.
Solution is to use prefix for your static content.
Example static URL that will work:
help/{PAGE_SLUG}
In this case make sure you does not have category with slug "help"