Auto-save is required for this to work. After sending your combat team to Outer Ops mission and you are using your mechs, the auto save will run and save your game. After the saving, Reports will notify you about the Mother Base. After the report, go to Outer Ops to view their Missions Status. If your Mech gets Decommissioned, (damaged beyond Repair), DO NOT SAVE MANUALLY. Instead, go to title screen without saving. Load your game again and it will return you to the Reports about the Mother Base, and after the Reports, Head to the Outer Ops again... Reset and Load until you receive a better outcome and your Mech is not Decommissioned.