skarasuko From what I understand, the key issue is the Query Behavior with active Keyframes in the Timeline.
When a deform timeline is applied, it checks the attachment in a single slot. If the deform timeline is for that attachment, it changes the vertices.
If the deform timeline could be applied to attachments in other slots, it would need to check those too. Disabling inherit timelines when a linked mesh is not in the same slot as the source mesh is probably the best solution.
skarasuko the biggest purpose of Linked Mesh in Different Slot is so we are able to readjust the Weights of our source Mesh.
A linked mesh uses the vertices and weights of its source mesh. Even if the linked mesh could be in a different slot, it would not work differently. The vertices and weights for a linked mesh are shared with the source mesh and cannot be modified separately. To do that, duplicate the mesh instead of using a linked mesh.
The mesh vertices define the position of the mesh in relation to the bound bones, or the slot's bone if none are bound. If a linked mesh could be placed in a different slot, it would appear in the exact same position as the source mesh and other linked meshes because it uses the same vertices and weights.
If no bones are bound and the linked mesh's slot is under a different bone, the linked mesh would be positioned relative to the slot's bone. That could make it appear in a different position, but that behavior may be somewhat surprising. If you changed the vertices or weights, the source mesh and all linked meshes change because the vertices and weights are shared.
Can you describe your use case more? I'm not sure a linked mesh in another slot is what you really want. In 4.2 the Weld feature can help you reuse weights for attachments like tattoos, clothing, etc.
In the post above by Huy137 I don't think linked meshes would help. If you setup the left arm with a mesh and weights, a linked mesh uses the same weights, so it'll be bound to the left arm bones. That doesn't help you with the right arm at all. I am wondering if there is any real use cases for linked meshes in other slots?
In 4.2 you can duplicate the left arm and Spine can duplicate all the bones, attachments, and constraints. You could then use that for the right arm, but changes to one side will not affect the other.
