When I check this on the property website of Belgium: CadGIS
It says it is part of that property, so unless that website is not correct it is indeed removed because it is part of single family private residential property.
Unfortunately, anything on that property even the edges is considered to be part of the property, see also the clarification here:
I don’t know about your specific situation but I have seen plenty of chapels that are not part of SFPRP. Maybe that is different in your area, that I don’t know.