Aim Offset freaking out when blended with Locomotion

I’ve added three images to this post and most of the explanation is in the description of those pictures. However, to quickly recap.

When I set up the Aim Offset everything looks as it should, but as soon as it is blended/added with the rest of the animation it freaks out completely. It looks to me a bit like the animation values have simply been added to the standard pose instead of just replacing the values/blending with them.

What could I try to do to fix this?