updateInvalidatedFastClusters (from what I know) will only run if a part/mesh gets de/parented under a model with a humanoid. Believe the only way around this is to not parent the skinned meshes under a character/humanoid or reduce the complexity
If these meshes aren’t under a humanoid, what I said above doesn’t apply
Edit: Based on this post, skinned meshes use fastclusters even if it is not in a humanoid. Documentation is missing this info