Hi Yvonnie,
Thanks for reaching out to us! I’d be happy to help you 🙂
According to the screenshots you’ve shared, you proceeded the right way to set up your recurring events series. That said, I created a recurring series on my local installation with a “once” exclusion but couldn’t replicate your issue.
So it’s likely there’s a conflict somewhere. Could you try to deactivate all other plugins, to see if that makes a difference? Could you also switch to the default theme (Twenty Seventeen)? Please read carefully our documentation about Testing for conflicts before doing anything.
Also, could you share your System Information? (you may set your reply as “Private”).
Cheers,
Jeremy