There are a couple of things you can try, one being uninstalling and re-installing the add-in through excel

If that does not work then you can try clearing the cache.
To clear the cache on excel if you are experiencing any difficulties and uninstalling excel does not resolve the problem, firstly make sure all close all office 365 applications - everything including excel, outlook, word etc.
Then press windows + R and type %LOCALAPPDATA%\Microsoft\Office\16.0\ then press enter. (as per the below screenshot)

Once the above command has been executed, you will then need to delete the folder 'Wef'

Once this has been done you can try running the report add in again to see if it works.
Should you still be experiencing any difficulties, please log a support ticket along with any relevant screenshots and information along with any steps you have taken so we can investigate further.