A 504 error occurs when the main server fails to provide a response within the established time limit. There are several possible causes that can lead to this error.
Among the likely factors is excessive load on the main server caused by high traffic. Slow script execution or database queries can also be a cause.
Other potential issues include incorrectly configured timeout parameters on the main server, which are set below the required level, as well as any network failures or delays in the network connection.
If this error occurs, users are advised to try again after some time.