Hey, first of all, you made a pretty good map!
Now here are three things that I noticed today:
I think there are are a few mistakes in your files:
The file sceneryobjects\OMSIBELGIQUE\Quai PMR\Bussteig DE.sco requests bussteg.o3d as the model. But the correct name would be bussteig.o3d
Just a simple typing error, but I think that caused the disapearance of a whole tile (No. 5, near Laisy Gare). Because after I had fixed it, the tile was there.
Another typing error, I think:
maptools told me that your map requests a sceneryobject named routearrows_butop.sco in the Generic-folder. The correct name would be routearrows_busstop.sco, wouldn't it? After I created a new file with the requested name, another few tiles apeared...
Now I think all tiles are there. I just had a little problem on the roundabout traffic at the bus stop Morlanbaix (line 8 near terminus Porchefontaine), when my bus stucked because of the shrubbery that is a little bit outside the fence.
Generally you need to check the routearrows because sometimes there is no information for some lines for a few crossings, and at some bus stops they don't say your line number altough you have to stop there.
Maybe you can fix some of those problems in one of your following patches. But maybe the disapeared tiles were also caused by my own mistake that I didn't notice? You'll se!
Overall your map is pretty good and when there are all tiles there, it can be many hours of fun driving on it 
