We import buildings and addresses from BAG, a government database. When the buildings are still marked as under construction on there, they're automatically imported as construction to OSM. Because they already appear on the map anyway, it sometimes causes buildings to stay as construction since buildings are not constantly checked by users. It is near impossible to track all the millions of buildings that exist in the Netherlands. I would say this is not necessarily a big problem. However, this seems like a noteworthy case as according to the BAG data, it was supposed to start construction in 2011. It is still marked as construction there. A callback on  their end would shed light on this.

https://bagviewer.kadaster.nl/lvbag/bag-viewer/?searchQuery=koksweg%209&objectId=0168200000233729&theme=BRT%20Achtergrond&geometry.x=261214.7015&geometry.y=483810.4815&zoomlevel=15