I have sent another file to Stan, so hopefully he can find what's going wrong. In the meantime I'm continuing to troubleshoot myself, experimenting with ways to isolate the problem.
I have prepared another video, in this video I have created a new bone and attached one of the arm muscles to it. I have also made another new bone and offset it to the side with a duplicate of the muscle. The issue consistently occurs around the same frames, with any tissue (new or old). Both of the new bones follow a locator that is constrained to the alembic bone. Is the solver struggling with this area in space?
Has anyone else had this kind of issue?
Could it be related to flipping somehow, it's as though the tissues change their collision direction.
I don't know if this is helps, but the issue does not occur when substeps are set to 1.
Any ideas would be super helpful, thanks