I think the contour lines are interpolated from discrete measurements, which can lead to strange effects especially on steep cliffs (I've seen overlapping contour lines too in some cases…).

As this is not an issue with the OSM data, and there is nothing that can be done to fix it in the OSM data, I'd opt to close this issue. You can always refer back to the issue by its URL (maybe add a bookmark in your browser), which will stay valid even when the issue is closed. Alternatively, you can find it again by going to your user profile, then click on "My Notes" (which will link to https://www.openstreetmap.org/user/Crsi/notes ).