GVM 20.08 Telnet vulnerability not detected

Hi All,
I’m using GVM 20.08 (built from source) and I’ve an issue when scanning a machine that runs a telnet server (linux telnetd).
GVM correctly detects the telnet service on port TCP23, but it does not raise the alert for the corresponding vulnerability (Telnet Unencrypted Cleartext Login).

Any help?
Many thanks in advance