With TLS 1.3 pre-shared key (PSK) a malicious or faulty server could ignore the request for PFS (perfect forward secrecy) and the client would continue on with the connection using PSK without PFS. This happened when a server responded to a ClientHello containing psk_dhe_ke without a key_share extension. The re-use of an authenticated PSK connection that on the clients side unexpectedly did not have PFS, reduces the security of the connection.
