bxl-forever
I get your point.  It looks more like a "rendering" issue than a "data" issue.

Other layers such as the Cycle Map ignore those stones and the name of the monument is visible there.
https://www.openstreetmap.org/#map=20/50.77043/4.40383&layers=C

I’ve tried a minor geometry fix, maybe it will help; otherwise if that is really a critical issue we should consider opening a ticket on osm-carto and ask to deal with cases like this.