originally i followed Reverse proxy - IIS (jenkins.io) to set up reverse proxy and it was all working fine until I upgraded to Jenkins 2.473.

from browser dev tools, I can see call is being made to 

GET

https://jenkins.mycompany.com/administrativeMonitor/hudson.diagnosis.ReverseProxySetupMonitor/testForReverseProxySetup/https%3A%2F%2Fjenkins.mycompany.com%2Fmanage%2F/ which returns 404

If i open this url in browser tab, i see message Oops! message with 

https://jenkins.mycompany.com:8080/manage vs. https://jenkins.mycompany.com/manage/

This page may not exist, or you may not have permission to see it.