This counts VRRP packets received with an invalid value in the packet's 'type' field, which per the VRRP protocol should only ever be the Advertisement type, so any other value indicates either a malformed packet, a corrupted transmission, or possibly a crafted/malicious packet. It's a lower-level protocol-integrity counter than the version or VRID error counters, catching cases where the packet claims a valid VRRP version and VRID but still fails basic protocol structure validation. A rising count here alongside otherwise-normal VRRP operation is worth flagging to a security team as a potential probing or fuzzing attempt against the VRRP implementation.