That doesn't have much to do with Florence: from the coordinates you posted and the screenshot, you were very close to the city of Cremona, at the intersection between the Po and Adda rivers, that is very far from Florence, about 180 Km north-west of it, well outside of the area covered by the scenery, which is about 12 km around the airport.
That bug is a typical mesh problem, at some place the altitude is wrong so, it's either a bug in the default mesh, or a bug in FS Global.