GPU at 100% when build but still have good FPS

Hello,

I have been trying for days to solve this problem and now I really need your help.

When I'm inside the editor and hit "play" the GPU is around 80% but when I build the project to test it, the GPU always stick between 99% and 100% and I still can't figure out what is happening.

I have found some possible solution like changing the "don't sync" to "every V band" and also tried the second V band.

I have also built the project with 0 vegetation at all and the problem still persist, which mean I have a feeling it has something to do with the textures of the terrain and it would make sense since it is mostly the only thing that changed since the last time the build was stable.

The map is a 2km * 2km
I use Vegetation Studio Pro (in a isometric view, I don't even need to see far)
Microsplat with tesslation module and anti-tile (those were added since the last stable version but turning them off don't change anything)
I have added texturing using substance, but again going back doesn't change anything.

Here a screenshot of the project and below some informations I get with the profiler.

All the help I can get would be very appreciated, I've stopped sleeping 3 days ago!