bxl-forever
Apparently, it is the 200-meter stretch between those two points:
https://www.openstreetmap.org/?mlat=50.90086&mlon=4.40626#map=17/50.90086/4.40626
https://www.openstreetmap.org/?mlat=50.90289&mlon=4.40943#map=17/50.90281/4.40947

There was a mistake in OSM data because it was considered as flowing in the open air all that time, which was obviously incorrect.

We should thank them for upgrading the infrastructure, because it matches OSM data now. 😃