WH is correct -
S106 agreement forms part of a specific planning permission, in this case the 2019 permission for the terminal extension. I believe the agreement is essentially an update to the agreement signed as part of the permission for the infill extension which was commenced by carrying out groundworks so that it didn’t lapse. However, the agreement contains provisions that if the 2019 extension is commended (works have been carried out to safeguard its validity) then the infill permission lapses.
The Council can only enforce the terms of the 2019 permission and its S106 agreement it cannot require additional measures beyond the scope of the permission and agreement.