Symptom 

When adding or removing Add-Ins the ribbon is not showing the changes. So new Add-Ins do not appear or removed Add-Ins are still visible in the Ribbon. 

Cause 

The Add-In cache is out of sync. 

Resolution 

Clearing the Add-In cache will trigger a re-sync of the Add-In cache. To clear the cache navigate to the cache folder (WEF) and delete all files within that WEF (cache) folder. 

You can find the folder here: %localappdata%\microsoft\office\16.0\WEF 

After clearing the contents of the WEF folder go and launch Word. This will trigger the re-sync of the WEF folder.