When you switch away from 'Build' mode, which deletes the node's joints, placeholder joints are created to preserve the character skinning until the node is rebuilt.
When you switch back to 'Build' mode, the node will know how to transfer the skinning back from the placeholders to the node joints.
When you reduce a node's number of joints, or delete or replace a node, the placeholder joints will remain, and you will need to manually transfer their weights.
Placeholder joints are placed in 'rig_root_grp'|'data_grp'|'placeholders_grp' hidden grp.
An indicator on the tools shelf will appear red when there are any placeholder joints.
The red indicator is not always indicative of a problem; a node temporarily switched to 'Template' mode will create placeholders until it is switched back to 'Build' mode. Check what's under 'placeholder_grp' if all your nodes are in 'Build' mode and the indicator is still red.
Manually transferring weights:
You can transfer skinning from a placeholder to any joint by selecting them in a zigzag order and using 'Helper Tools' -> 'Transfer Weights (Placeholder ->Joint)'
In the event that a node is deleted, but a new node of the same type and name is created after, the weights of the old node placeholders will not be automatically transferred to the new one.
For example, deleting the node 'R_Leg' and then duplicating and mirroring the 'L_leg' node, so a new node named 'R_Leg' is created (Which is helpful if you also want to copy the node attributes and attachments).
You can then transfer weights by using the 'Transfer Placeholders Weights By Name' from the 'Helper Tools' section.
When doing this, make sure that the newly-created node is in 'Build' mode since its joints must exist.
_____________________________________________
Get Arise at: https://www.ariserigging.com