You have created an org structure and activated some parts of the org structures. However, you have observed that the unactivated org units are missing in the planning area of the Org structure.
The cause for the issue might be that, you have performed a Roll back in the planning area.
The roll back function irreversibly deletes all organisational units that had not yet been activated.
The solution is to re-create the missing organisational units as of the desired key date and afterwards move the units/structure via the Cut and Paste operations under the existing units so that the structure looks as originally desired.
KBA , SRD-MD-OM , Organizational Management , How To