I don't have any of the sceneries mentioned, but I can take a stab at this question.
It's not your system, it's the limitations of the sim. The big challenge is the 32 bit container that cannot manage the complexities of the technology we are loading into our simulations. Your card is not being utilized to it's full potential and the sim cannot handle the staggering number of calls when facing any particular direction.
I will assume that there are a gozillion individually modeled buildings in this scenery, much to the author's credit. This is a massive amount of work that has been put into this package. I'd be keen to see the actual file size and .bgl model library for the Miami scenry...it would tell me a lot. If it's over one gig...it's a monster.
I would guess that when the sim is looking down the barrel of this scenery it is loading a ton of custom buildings and autogen, along with hand painted and photo real ground polys while simultaneously running weather, geo spatial mesh and a sophisticated aircraft.
There are tricks to building ultra complex sceneries and they all need to be integrated into the working model with the broadest applicability to find a balance of realism and performance, while satisfying the broadest spectrum of home simulator computers. It's not easy, and quite frankly most developers tend to design thinking forward...myself included. When we are looking at an imminent 64 bit platform, designing for 32 bit becomes prohibitive. That said, all developers realize and acknowledge that 32 bit will always represent a large market segment, thus it cannot be entirely abandoned. This is a paradox that will remain with us for quite some time.
The phenomenon your are showing appears to be the sim looking to load a specific ground poly, possibly masked in at a higher resolution than the surrounding blocks. In the background the sim is also loading everything else as well. The autogen seems to be loading, but what appear to be custom buildings with textures and possibly a modeled freeway section have failed to call their textures. The black area is not loading the ground poly, the buildings are not loading what I would predict would be custom textures.
From what I see in your screen cap, I would bet money that the entire city has been hand annotated with individually placed autogen buildings and trees placed correctly on top of the photo realistic ground poly. This is absolutely the best way to create an entirely accurate model, but very costly for the sim in terms of resources required.
At the point this happens your system has hit the VAS wall and your card, governed down to 32 bit, is screaming WTF? The cause is primarily based on the direction of your point of view and the targets down range. This would explain the random nature of the display anomaly. Facing any given direction this could happen. This could theoretically occur even if you had not logged mileage over other scenery prior to flying in the megalopolis.
All major cities will be vulnerable to this display anomaly and performance will depend solely upon how the model was constructed.
Example: I simply cannot fly the CS or PMDG Boeing 777 into NCA/Flightbeam KSFO...it just won't happen. Too much is being asked of the 32 bit framework, even though my system is a rock crusher. These are all magnificent aircraft/sceneries, but the sum total of the resources required are huge.
My consolation is that a 64 bit platform seems to be right around the corner, so I'd enjoy the scenery for now and forget about all of these inconveniences when we are able to take better advantage of the systems we have invested so much time and $$$ into constructing.
Don't lose any sleep my friend...the solution is near.
Devs will suggest either reducing background processes and/or reducing your graphic settings. I honestly can't see the point of reducing the graphic settings if you miss a whole bunch of what you want to see!!
