Thank you for the log and Wireshark capture.
The Rebex log showed that the server really returned alert 0x70 (UnrecognizedName), which means: Sent by servers when no server exists identified by the name provided by the client via the “server_name” extension (see [RFC6066]).
It also showed, that you are trying to establish TLS 1.3.
The Wireshark capture showed that the system is trying to negotiate TLS 1.2.
The content of the “server_name” extension is same as in Rebex, which means the server is "lying" when sending UnrecognizedName alert in Rebex case.
It is probable that the server is handling TLS 1.3 ClientHello incorrectly. Please, try to disable TLS 1.3 by setting SslAllowedVersions like this:
creator.Settings.SslAllowedVersions = TlsVersion.TLS12;