Boxcollider is much bigger than the actual Object (imported from Blender)

I have created a 3D model in Blender and included the .fbx in my Unity project. But the BoxCollider looks like the following:

I also tried the same with a MeshCollider, but the output of localScale is always 0. In the import settings “Generate Colliders” is activated. Does anyone know how to fix this issue?

Open the GameObject of the collider and adjust manually the box collider size on the Component

Try unchecking the button near scale when exporting to .fbx, if that does not help try recreating the object bit by bit and uploading it to unity at each step, maybe that will help you figure out where the exact problems starts.