Hi,
This object seems to be a building but you have removed the tag building=yes from it. Therefore it is no longer rendered like a building.
You have replaced the building tag with tag leisure=horse_riding, but this tag is not for buildings, it is for complete riding centres, see https://wiki.openstreetmap.org/wiki/FR:Tag:leisure=horse_riding and https://www.openstreetmap.org/way/817128685 (example).
If the building is an indoor arena you can use tag building=riding_hall, example: https://www.openstreetmap.org/way/146763960