The only fix that worked for me on my end was changing the Excel output to a Flat File CSV. Once I had done that, the package ran fine.

Thanks for the reponse! I forgot to update my post. I ended up finding that I had that unchecked. I went ahead and checked that and restarted the SQL Server...

Did you ever get this resolved? I am running across the same issue. SEND TEST E-MAIL works in the DB Mail Configuration but the Notifications are not working.