Hi, i work in a small team of non-commercial mod-makers, and we encountered very specific problem, which doenst have an easy answer in web.
So there is a level with world partition, and a landscape. Somebody drafted some time ago a lot of roads via Landscape Splines, and applied temporary meshes to it, so everybody knew where roads should be.
After some time i decided to apply more visualy appealing meshes, and do some work with visuals. It is hard to track at which point problems started, so its hard to debug.
Right now actual mesh shows only in editor, without any problem, and without other meshes on top of it. But in PIE (or any “game modes”) actual mesh not exist, but previous one (from draft-era) shows without any reason. Btw landscape seems to deform according to current Landscape Splines.
I tried a lot of things and settings, cant even list them all. Any switch that exist in “details” of Landscape spline (or sections/segments in Landscape edit mode) was turned on/off with testing in PIE - it did nothing.
More to say - i even deleted Landscape spline actors, but old mesh keep showing in places, where it was.
Please dont tell me to check if “Hidden in game” or “Dont draw in main pass” (or similar) are on, it was double-triple-andmore checked. Aswell as clearing DDC, “Saved” folders etc. Problem appear for any member btw.
Have to say - we tried building HLODs at some point, but rejected because of time that is needed for full build. However i tried to delete HLODs through “build->hlod” menu several times, when i tried to fix this road-problem.
Please, if you have any idea what it can be - share, because im out of mine 
In editor
In PIE
edit. in pie there even a collision for an old mesh, which is not affected by collision options in Landscape spline actor (even deleting this actor doesnt affect collision for an old mesh in PIE)
upd. Nvm guys, its just an eternal classic of overcomplicating problems. I just didnt knew that u can go “Build-> Build landscape spline meshes”. So apparently someone from team did build them, and went silent about that.
Dont know how to summon mods, but i cant close topic by myself.