We found that if proxy_intercept_errors is configured as on in the Nginx (the reverse proxy for Confluence), Synchrony does not work properly – when user creates a new page, the page stays hanging with a spinning sign.
This is due to that Synchrony returns 404 when user creates a new page, and the proxy_intercept_error tries to redirect users to a pre-defined error page for 404. Details can be found here: CONFSERVER-46487
The solution is either set Synchrony to limited mode (only one person can edit each time), or set proxy_intercept_error to off.
Jackie Chen's IT Workshop 