hello i have the same
kind off . i have a big size Terrain and i sculped it and Paint it and out of the Blue its started Glitching in the Viewport
and at loading a session you fall at some parts of the map.
but its as well not consistent everytime i load in UEFN or a new session the issue skip possition
I recognise as well that it takes over the terrain collission of a neighbor Terrain
And then Sometimes it just work with a “Push Changes” just fine and after one more time “Push Changes” not anymore again.
Quite annoiing.
I used Hydro onf the Trerrainpieces to try but it did not effect anything.
and the collission is on somewhere up or below. then i can run in the air or run thru all the terrain (hills and above holes)