Related threads:
https://forum.corona-renderer.com/ Corona's SSS behavior with multi/sub-object material and IDs
https://forum.corona-renderer.com/ Beta 2 Skin Shader Seaming
https://forum.corona-renderer.com/ C4D Seam Issues with SSS
There is a workaround by Nekrobul [3ds max]: instead of using 2 different material IDs directly, use a Blend material, connect the two SSS materials to it, and blend them using a mask (for example CoronaMultiMap). Will test and confirm if it works.
Another workaround: use CoronaMultiMap: https://forum.corona-renderer.com/ Corona's SSS behavior with multi/sub-object material and IDs #msg134584