I am encountering the same problem, but without it redirecting to a strange address.
Following the instructions in this thread did not help, but also, none of the commands generated any errors.
The log shows:
2018/10/11 15:10:07 [error] 9573#0: *7 open() "/usr/local/cwpsrv/var/services/users/login/index.html" failed (2: No such file or directory), client: *******, server: localhost, request: "GET /index.html?username=cloudope&password=******* HTTP/1.1", host: "*******:2083", referrer: "https://*******4:2083/"
2018/10/11 15:11:14 [error] 9573#0: *22 open() "/usr/local/cwpsrv/var/services/users/login/index.html" failed (2: No such file or directory), client: *******, server: localhost, request: "GET /index.html?username=cloudope&password=******* HTTP/1.1", host: "h03.*******.com:2083"