The send file support is not available when NCP encryption is set to enable or enforce. So any setting to SENDFILE_SUPPORT is ineffective when encryption is set to enable or enforce.
Modifying the Advanced Authentication settings on the Client for Open Enterprise Server from enable to disable when the security Enforce-MFA is set to Yes on the NCP server does not take effect and block the client server connection. For the Client setting to take effect, restart the Client after changing the Advanced Authentication settings.