We are having some issues with blend masks and compatible skeletons. We have skeleton A as the base and skeleton B as a compatible skeleton. They both share a similar hierarchy (although not identical) We have a blend mask in skeleton A and use the node LayeredBlendPerBone (blendmask) with such mask in an ABP that will use skeleton B. We can see the blend mask is cached with the bone indexes of skeleton A. The blend mask is applied by bone index to skeleton B and since skeletons are not identical we don't get the correct behavior.