Cannot refresh when dashboard filter contains non-alphanumeric (e.g., @)

I created a dashboard filter to sort people by email address. While it works, it cannot be refreshed because the @ sign in the email gets converted into %20 in the url (happens even when I refresh it using the dashboard’s own refresh button).

Is there a fix for this?

Separately. I realized that I’m having difficulty creating filters on parameters that are joined to my main table. Is that true?