What issue ?
The "cliff" cannot be avoided because, since as explained so many times in the forum, the sim doesn't really support sloped runways, so it must have the same altitude along the entire airports, which means a very gentle down slope like this cannot be made, so the coastline will have some kind of cliff effect.
And, I don't see any flickering problem or black textures you describe, so it must be surely due to one of the many other 3rd party sceneries you have installed.