Page Not Found - Check the url

New FESS 12.0 + separate ES 6.1.1 install.

On the front-end search UI, clicking on any result leads to a FESS page that says:

Page Not Found
Check the url.

I don’t see anything relevant in the logs. Any ideas on what the issue is?

Could you check fess.log after changing a log level to debug?
The log level is in[sh|bat].

FESS_JAVA_OPTS="$FESS_JAVA_OPTS -Dfess.log.level=warn"

Thanks, that pointed me to the IIS reverse proxy we are using. Still troubleshooting, but it appears there is some trickery happening with the URL rewrite settings that is causing this.