First, please let each user run the Office 365 Desktop Setup on their computer:
Sign in MOP, click Downloads, and click the button Set up under Set up and configure your Office desktop apps.
If this issue persists, you can use OSAUI.exe /K to reset and reactivate Office Professional Plus:
1. Click Start, type cmd in the search field, press Enter.
2. Run OSAUI.exe /K, you can locate OSAUI.exe from C:Program Files(x86)Common FilesMicrosoft SharedOFFICE14.
Then, it will prompt for user’s Office 365 ID and password and let Office 365 service retrieves a new product key.
If the commands above don’t work, please try OSAUI.exe /F to see if it works.