What are some common reasons why a Cloudflare IP scanner might show an IP address as 'dirty' or blocked?

An IP address can be flagged as 'dirty' due to several reasons: it's on a known blacklist (spam, malware), it's been associated with abusive behavior (DDoS attacks, bot activity), it's a residential proxy IP, or Cloudflare's own security rules have identified it as suspicious. It's also possible your own firewall rules are blocking the scanner's requests.