TL;DR How can I get around the dependency loop between parented bones with an IK in between, without having to delete the IK element? The rig should be switched between IK and FK by changing the influence slider.
I have a body with an IK set up. I have a driver which changes the influence of all IK elements (and some Child Of constraints) between 1 and 0 so that the IK and FK can be switched between. This works in all places apart from the spine.
I cannot get 'Spine 3' to be the child of 'Spine 2'. Spine 2 is the part with the IK applied to it.
This method works in other places because, when the influence is at 1, the IK takes over; with the FK taking over when influence is at 0. The lower arms and lower legs still parent to the upper arms and legs, but this parenting is not allowed in the spine - even though, to me, it appears to be the same as parenting the arms and legs.
I'm aware of the issue of a dependency loop which Blender is preventing from happening. But how can I override this/what is the work around? It works if I just delete the IK in the spine, but this is essentially what is happening when I set the influence to 0.