[Johan Meijer]

No, I did not apply 2 LUTs to 1 clip, I removed the LUT from the clip before applying it to the node. But it is probably a bug in the software. I started a new project and now it works!
Or maybe it had something to do with the fact that the project was set at 24 fps, while the input file was 60 fps. In the new project I set the project at 60 fps (which I found out is the very first thing you should do in a project).