Baked impostors do this commonly when the material used for them is created by the engine - the specularity and roughness values are just set to .5 which often doesn’t match the landscape when combined with the screenshot the impostor system takes.
To fix it you have to manually take a roughness and specularity image and use those instead of a value of .5
Gruesom process when dealing with hundreds of tiles…
So if found out it is indeed a landscape material problem. The material i am using is quite a complicated selfbuild mess so when i painted a certain layer on it it changed the specular for ALL layers somehow and this only happens inside the tile it is painted in which is quite the funny effect.