As has already been explained in the answer on help.openstreetmap.org changes to relations do not trigger automatic re-rendering - the reason for that is that analysing relations to work out what tiles they affect is hard to do and potentially very expensive and in the worst case you might wind up marking very large numbers of tiles as dirty and having to re-render them.
Low zoom tiles (zooms 1-12) are never dirtied anyway and are instead just re-rendered once a week.
Zooms above that are re-rendered when we think a node or way that impacts them has changed - strictly speaking they are marked as dirty at that point, and we will try to re-render them the next time somebody asks for them.