This is what the error log shows:
2019/02/17 11:08:13 [error] 18533#0: *3396 open() "/opt/psa/admin/htdocs/robots.txt" failed (2: No such file or directory), client: 54.174.61.199, server: , request: "GET /robots.txt HTTP/1.1", host: "whm.celeratec.com:8443"
2019/02/17 11:10:11 [error] 18533#0: *3416 open() "/opt/psa/admin/htdocs/robots.txt" failed (2: No such file or directory), client: 54.174.58.201, server: , request: "GET /robots.txt HTTP/1.1", host: "whm.celeratec.com:8443"
2019/02/17 18:57:39 [crit] 18533#0: *4349 SSL_do_handshake() failed (SSL: error:1417D18C:SSL routines:tls_process_client_hello:version too low) while SSL handshaking, client: 216.218.206.69, server: 0.0.0.0:8443
2019/02/18 19:05:22 [error] 18533#0: *6142 open() "/opt/psa/admin/htdocs/robots.txt" failed (2: No such file or directory), client: 35.231.112.211, server: , request: "GET /robots.txt HTTP/1.0", host: "whm.celeratec.com:8443"
2019/02/18 19:05:56 [crit] 18533#0: *6147 SSL_do_handshake() failed (SSL: error:1417D18C:SSL routines:tls_process_client_hello:version too low) while SSL handshaking, client: 184.105.139.68, server: 0.0.0.0:8443
2019/02/18 20:40:56 [crit] 18533#0: *6149 SSL_do_handshake() failed (SSL: error:1417D0A0:SSL routines:tls_process_client_hello:length too short) while SSL handshaking, client: 108.178.16.154, server: 0.0.0.0:8443
2019/02/19 17:58:39 [error] 18533#0: *7329 open() "/opt/psa/admin/htdocs/robots.txt" failed (2: No such file or directory), client: 104.196.127.42, server: , request: "GET /robots.txt HTTP/1.0", host: "whm.celeratec.com:8443"
2019/02/19 19:14:47 [crit] 18533#0: *7338 SSL_do_handshake() failed (SSL: error:1417D18C:SSL routines:tls_process_client_hello:version too low) while SSL handshaking, client: 74.82.47.5, server: 0.0.0.0:8443
2019/02/20 05:32:46 [error] 18533#0: *7369 open() "/opt/psa/admin/htdocs/robots.txt" failed (2: No such file or directory), client: 66.249.69.8, server: , request: "GET /robots.txt HTTP/1.1", host: "whm.celeratec.com:8443"
2019/02/20 12:24:00 [error] 18533#0: *7522 open() "/opt/psa/admin/htdocs/robots.txt" failed (2: No such file or directory), client: 157.55.39.21, server: , request: "GET /robots.txt HTTP/1.1", host: "whm.celeratec.com"
2019/02/20 18:44:16 [crit] 18533#0: *7534 SSL_do_handshake() failed (SSL: error:1417D18C:SSL routines:tls_process_client_hello:version too low) while SSL handshaking, client: 74.82.47.3, server: 0.0.0.0:8443
2019/02/20 20:37:05 [error] 18533#0: *7536 open() "/opt/psa/admin/htdocs/robots.txt" failed (2: No such file or directory), client: 66.249.73.71, server: , request: "GET /robots.txt HTTP/1.1", host: "whm.celeratec.com:8443"
2019/02/21 00:43:23 [error] 18533#0: *7539 open() "/opt/psa/admin/htdocs/robots.txt" failed (2: No such file or directory), client: 35.227.16.80, server: , request: "GET /robots.txt HTTP/1.0", host: "whm.celeratec.com:8443"
2019/02/21 11:50:47 [error] 18533#0: *7549 open() "/opt/psa/admin/htdocs/robots.txt" failed (2: No such file or directory), client: 66.249.79.103, server: , request: "GET /robots.txt HTTP/1.1", host: "whm.celeratec.com:8443"
2019/02/21 14:04:55 [error] 18533#0: *7556 open() "/opt/psa/admin/htdocs/robots.txt" failed (2: No such file or directory), client: 34.73.100.99, server: , request: "GET /robots.txt HTTP/1.0", host: "whm.celeratec.com:8443"