The Office Timeline tab is missing from the PowerPoint ribbon whenever PowerPoint is restarted. This occurs despite Office Timeline being listed on the Active Application Add-ins list (File-> Options-> Add-Ins) in PowerPoint.
When installed, Office Timeline attempts to create a series of registry keys with specific values that allow the add-in to operate properly. Sometimes, the LoadBehavior registry keys are not properly set which restricts Office Timeline from loading correctly. Accessing RegEdit and restoring the registry key fixes the behavior described above.
Press the Windows key on your keyboard to open windows search and type Regedit to open the Registry Editor.
Navigate to HKEY_CURRENT_USER > Software > Microsoft > Office > PowerPoint > Add-ins > OfficeTimeline > LoadBehavior
Double click the “LoadBehavior” key and change the Value data to “3” .
See video of these steps: