This can also happen when you are after an update and revisit a place you last visited before the update. Something to try: remove your cache file, leave the game, restart the game and make a new cache file. Also check the Bing option. When it is not on, it won’t refresh. At first, you’ll have a lower frame rate because the cache is being refilled.
It could also be an issue with third party scenery. They changed the elevation scaling. Only thing you can do in that case is remove the scenery, from Community or via Content Manager in Profile… Check this