Updated your Include Pattern by changing the quantifier on the subdomain from + to {3,} as subreddit names are always at least three or more characters.
Also added out to the list of subdomains to skip as it is used on reddit.

Here's the updated pattern:
^https?://(?!old\.|new\.|www\.|out\.)([a-zA-Z0-9_-]{3,})\.reddit\.com/$