Hi,
You have retagged this area from a building (building=yes) to a horse riding centre (leisure=horse_riding); now it is no longer rendered like a building. But this object is a building and not a horse riding centre, so it should have a building=* tag. If it is an indoor arena (for horse riding) you can use https://wiki.openstreetmap.org/wiki/Tag:building=riding_hall .
The tag leisure=horse_riding should not be used for single buildings of a riding centre but for the whole riding centre, either as an area like here: https://www.openstreetmap.org/way/1013100518, or as a node like here: https://www.openstreetmap.org/node/7890409852. Compare https://wiki.openstreetmap.org/wiki/How_to_map_a#Riding_centre_(equestrian)