Taking off from Madrid (LEMD) to Faro (LPFR) just now came across this in the SE. Last time I have seen this was in P3D.
Ouch!
I would suggest to delete SceneryIndexes folder and let game rebuild it. This looks like a kind of scenery artifact.
Cheers
Before posting, please search the forum to see if there is an existing topic.
https://forums.flightsimulator.com/t/ground-or-terrain-spikes/367615
Assure no addons are used that can alter scenery, terrain or seasons.