bxl-forever
@oposm
This is not a data problem—the multipolygon is fine—but a rendering problem.
Other layers and many third-party apps show both parts of the park correctly.

This is a known issue in osm-carto: https://github.com/gravitystorm/openstreetmap-carto/issues/1136
In fact, the park is rendered… then the gray landuse=residential area is rendered on top of it.  This is because the landuse area is considered smaller than the (overall) park.

A quick and dirty solution would be to delete the landuse area, but it would feel like tagging for the renderer.