After upgrading the appliance to version 5.11.0 and higher some RDP connections do not build up.
The exact error message in the logs:
SSL handshake failed; side='server', error='error:14171102:SSL routines:lib(20):tls_process_server_hello:func(369):unsupported protocol:reason(258)
From firmware version 5.11.0 the default SSL setting for RDP proxy is to use TLS version 1.2. This can cause trouble on RDP servers or clients which do not support this.
Please either upgrade or reconfigure the RDP servers/clients to use TLS 1.2
It is also possible to reconfigure TLS settings on SPS appliance.
To do so please go to RDP Control -> Settings -> [setting name] and scroll down to TLS security settings.