Imported animation has small rotation offset

I’m importing a set of animations to make an aim offset for my character, so I need the rotations to be precisely of 90 degrees in all directions.
The problem is that the rotations I have on my exported fbx are not precisely the same on the animation in unreal, as you can see below, in this case, there is roughly a 0.67 difference on the z axis which is carried in all the animations (so if I import an animation with 0,0,90 I end up with 0,0,90.67)

Does anyone know what might cause this problem?