This started happening to me when i had Nodebb Running on a server behind Nginx as a reverse proxy in multiple processes. Funny enough it worked okay with conventional setup where nodebb was running in one port and process. Ultimately following Nginx config file helped me resolve the issue.
Background of 400 Bad Request Error
The 400 Bad Request Error is an
HTTP response status code that indicates that the server was unable to process the request sent by the client due to invalid syntax. As with the dozens of potential HTTP response codes, receiving a
400 Bad Request Error while accessing your own application can be both frustrating and challenging to fix. Such HTTP response codes represent the complex relationship between the client, a web application, a web server, and often multiple third-party web services, so determining the cause of a particular status code can be a difficult, even within a controlled development environment.