SFTP fails at negotiation (old version of Rebex SFTP)

We are trying to connect to an SFTP server that uses ECDH key exchange with curve nistp256 and hash SHA-256 (SHA-NI accelerated) and it fails at negotiation. Here is the Rebex logs:

2022-07-28 11:02:13.177 Opening log file.
2022-07-28 11:02:13.178 INFO FileLogWriter(1)[38] Info: Assembly: Rebex.Common 2017 R6.2 for .NET 4.0-4.7
2022-07-28 11:02:13.178 INFO FileLogWriter(1)[38] Info: Platform: Windows 6.2.9200 32-bit; CLR: 4.0.30319.42000
2022-07-28 11:02:13.178 DEBUG FileLogWriter(1)[38] Info: Culture: en; Windows-1252
2022-07-28 11:02:40.307 INFO Sftp(7)[38] Info: Connecting to xxx:22 using Sftp.
2022-07-28 11:02:40.307 INFO Sftp(7)[38] Info: Assembly: Rebex.Sftp 2017 R6.2 for .NET 4.0-4.7
2022-07-28 11:02:40.307 INFO Sftp(7)[38] Info: Platform: Windows 6.2.9200 32-bit; CLR: 4.0.30319.42000
2022-07-28 11:02:40.318 DEBUG Sftp(7)[38] Info: Culture: en; Windows-1252
2022-07-28 11:02:40.318 DEBUG ProxySocket(4)[38] Proxy: Resolving 'xxx'.
2022-07-28 11:02:40.442 DEBUG ProxySocket(4)[38] Proxy: Connecting to none proxy at xxx.xxx.xxx.xxx:22.
2022-07-28 11:02:40.705 DEBUG Sftp(7)[38] SSH: Server is 'SSH-2.0-mod_sftp/0.9.9'.
2022-07-28 11:02:40.706 INFO Sftp(7)[38] SSH: Negotiation started.
2022-07-28 11:02:40.707 DEBUG Sftp(7)[38] SSH: Negotiating key.
2022-07-28 11:02:40.836 DEBUG Sftp(7)[17] SSH: SSH connection closed.
2022-07-28 11:02:40.842 ERROR Sftp(7)[38] SSH: Negotiation failed. The connection was closed by the server.
2022-07-28 11:02:40.843 ERROR Sftp(7)[38] Info: Rebex.Net.SshException: The connection was closed by the server.
   at Rebex.Net.SshSession.XIA[I,O](SQI`2 I, Int32 O, RQI J, O D, I B, I N)
   at Rebex.Net.SshSession.XIA[I,O](SQI`2 I, O O)
   at Rebex.Net.SshSession.JIA(KQI I)
   at Rebex.Net.LQI.C(SshSession I, Byte[] O, Byte[] J, Byte[] D, Byte[] B, PQI& N, Byte[]& C, SshPublicKey& M)
   at Rebex.Net.SshSession.NIA(Byte[] I)
   at Rebex.Net.SshSession.Negotiate()
   at Rebex.Net.Sftp.MRI.NIA(ARI I, Boolean O)
   at Rebex.Net.Sftp.UD(String I, Int32 O, SshParameters J, ARI D)

Here is the trace log from Filezilla successfully connecting:

Trace:  CControlSocket::SendNextCommand()
Trace:  CSftpConnectOpData::Send() in state 0
Status: Connecting to xxx...
Trace:  Going to execute C:\Program Files\FileZilla FTP Client\fzsftp.exe
Response:   fzSftp started, protocol_version=11
Trace:  CSftpConnectOpData::ParseResponse() in state 0
Trace:  CControlSocket::SendNextCommand()
Trace:  CSftpConnectOpData::Send() in state 3
Command:    open "xxx" 22
Trace:  Looking up host "xxx" for SSH connection
Trace:  Connecting to xxx.xxx.xxx.xxx port 22
Trace:  We claim version: SSH-2.0-FileZilla_3.60.2
Trace:  Connected to xxx.xxx.xxx.xxx
Trace:  Remote version: SSH-2.0-mod_sftp/0.9.9
Trace:  Using SSH protocol version 2
Trace:  Doing ECDH key exchange with curve nistp256 and hash SHA-256 (SHA-NI accelerated)
Trace:  Server also has ssh-dss host key, but we don't know it
Trace:  Host key fingerprint is:
Trace:  ssh-rsa 2048 SHA256:PZyJ2DNQ3JGaqn5MjD3u79EdaQ+vSLMGjJYNHELbTOY
Trace:  CSftpControlSocket::SetAsyncRequestReply
Command:    Trust new Hostkey: Once
Trace:  Initialised AES-256 SDCTR (AES-NI accelerated) outbound encryption
Trace:  Initialised HMAC-SHA-256 (SHA-NI accelerated) outbound MAC algorithm
Trace:  Initialised AES-256 SDCTR (AES-NI accelerated) inbound encryption
Trace:  Initialised HMAC-SHA-256 (SHA-NI accelerated) inbound MAC algorithm
Status: Using username "xxx". 
Command:    Pass: ********
Trace:  Sent password
Trace:  Access granted
Trace:  Opening main session channel
Trace:  Opened main channel
Trace:  Started a shell/command
Status: Connected to xxx
Trace:  Remote working directory is /
Trace:  CSftpConnectOpData::ParseResponse() in state 3
Trace:  CControlSocket::ResetOperation(0)
Trace:  CSftpConnectOpData::Reset(0) in state 3
Trace:  CFileZillaEnginePrivate::ResetOperation(0)
Trace:  CControlSocket::SendNextCommand()
Trace:  CSftpListOpData::Send() in state 0
Status: Retrieving directory listing...
Trace:  CSftpChangeDirOpData::Send() in state 0
Trace:  CSftpChangeDirOpData::Send() in state 1
Command:    pwd
Response:   Current directory is: "/"
Trace:  CSftpChangeDirOpData::ParseResponse() in state 1
Trace:  CControlSocket::ResetOperation(0)
Trace:  CSftpChangeDirOpData::Reset(0) in state 1
Trace:  CSftpListOpData::SubcommandResult(0) in state 1
Trace:  CControlSocket::SendNextCommand()
Trace:  CSftpListOpData::Send() in state 2
Trace:  CSftpListOpData::Send() in state 3
Command:    ls
Status: Listing directory /
Trace:  CSftpListOpData::ParseResponse() in state 3
Trace:  CControlSocket::ResetOperation(0)
Trace:  CSftpListOpData::Reset(0) in state 3
Status: Directory listing of "/" successful
Trace:  CFileZillaEnginePrivate::ResetOperation(0)

We have manually registered the additional elliptical curve algorithms in our code with:

AsymmetricKeyAlgorithm.Register(EllipticCurveAlgorithm.Create); 
AsymmetricKeyAlgorithm.Register(Curve25519.Create); 
AsymmetricKeyAlgorithm.Register(Ed25519.Create);

Along with registering those encryptions, we set Rebex to allow any type with:

var newConnection = new Sftp
{
    Settings = new SftpSettings
    {
        SshParameters = new SshParameters { AuthenticationMethods = SshAuthenticationMethod.Any, EncryptionAlgorithms = SshEncryptionAlgorithm.Any, HostKeyAlgorithms = SshHostKeyAlgorithm.Any }
    },
    LogWriter = logWriter
};