So, i unwrapped my object in 3ds max, and imported it in unity.
In unity, the texture is stretched with some kind of arrows, while in 3ds max it is not.
I have found this post on polycount about triangulating, which I did, but that also did not solve the problem: https://polycount.com/discussion/213917/texture-stretching-distortion-when-importing-to-unity
Does anyone know what this is about?
[ Found the solution in the meantime: The problem was the height map, I just deleted that and everything is fine now. Adding this for people that might need it in the future. ]