When deployed under Tomcat, Jenkins requires to have this option set :

-Dorg.apache.tomcat.util.buf.UDecoder.ALLOW_ENCODED_SLASH=true

This is a known issue/limitation/prerequisite like described in:

• https://wiki.jenkins-ci.org/display/JENKINS/Tomcat
• JENKINS-21335

The reverse proxy monitor was verifying this originally ( info confirmed by jglick ) :
https://github.com/jenkinsci/jenkins/commit/724f9e0dfc2011d4c12e867bd85bc3f32c2b0513 (1.552)

But it was lost in this commit: https://github.com/jenkinsci/jenkins/commit/cffe9df0176b0ff895554ce7f2ea4d2f20062351 (1.572)

I'm not sure that all these controls should be in the same monitor but for sure the test must be done.

Maybe:

• to be re-added in the reverse proxy monitor to verify when the problem comes from the reverse proxy.
• to be re- added as a specific Monitor for Tomcat because if org.apache.tomcat.util.buf.UDecoder.ALLOW_ENCODED_SLASH isn't set it will break some Jenkins features (400 HTTP Error - Bad Request with AJAX calls inside Folders for example, ...) even if there is no reverse proxy configured.