This counts HTTP requests blocked for containing non-ASCII or malformed character encoding where standard ASCII encoding is expected. Attackers use non-standard encoding specifically to evade signature-based inspection or smuggle exploit payloads past filters that only pattern-match plain text, so this counter is a proxy for that evasion technique being attempted against the web servers behind this gateway. For example, a request using overlong UTF-8 encoding to disguise a SQL-injection payload getting caught and counted here.