Users unable to connect to JSC VPN due to "Empty reply from server" error
Configuration under [edit security remote-access] may be incomplete or missing, this causes the users to receive an "Empty reply from server" after SSL authentication.
After SSL authentication (certificate validation) clients will try to download IKE and IPsec configuration from the SRX in order to establish IPsec tunnels, if remote-access is not properly configured users may receive this error.
Configure security remote-access as per https://www.juniper.net/documentation/us/en/software/secure-connect/secure-connect-administrator-guide/topics/task/local-authentication-with-local-ip-pool-cli-procedure.html.
11-9-2023: Title modified to be more specific with the KB content.
https://www.juniper.net/documentation/us/en/software/secure-connect/secure-connect-administrator-guide/topics/task/local-authentication-with-local-ip-pool-cli-procedure.html
https://www.juniper.net/documentation/us/en/software/secure-connect/secure-connect-administrator-guide/topics/task/secure-connect-vpn-using-IKEv1-radius-cli-procedure.html