Can't remove slump in the terrain

I'm using ORBX scenery in FSX:SE
On my favorite airport, EBBL, there is a slump in the terrain but at the wrong place.
I have tried many changes in the design of the airport but nothing helps.
The ORBX Open LC Europe 4 was deactivated already.
I even tried to change the coordinates of the airport.
How can get rid of this ?