I'm not sure what's happening, but I have some information and a troubleshooting step that may help:
The "Resource not found" error is generally a result of insufficient disk space on the Tableau server machine. Try running a tabadmin cleanup and restarting the Tableau Server machine(s).
Http 404 - File not found errors are sometimes encountered when attempting to configure trusted authentication because the program code references a Tableau Server URL that does not exist. More info here.
Additionally, sometimes issues connecting to Tableau Server through an SSL proxy are resolved by configuring the proxy server to forward the X-Forwarded-Proto HTTP header. More information here.
I hope that helps.