I've seem recently this 404 issue in one of the jenkins instances I do manage, but also in the https://ci.jenkins.io one.

Error message:

HTTP ERROR 403Problem accessing /blue/rest/classes/. 
Reason:    No valid crumb was included in the requestPowered by Jetty:// 9.4.z-SNAPSHOT

Screenshots:

But it works perfectly fine when accessing the traditional view:

How to reproduce locally?

• Open an incognito browser
• Open a BO URL
• Repeat the same with the traditional view

Workaround?

• Refresh
• Use -Djenkins.displayurl.provider=org.jenkinsci.plugins.displayurlapi.ClassicDisplayURLProvider

Even though there is a workaround I'd say it's not a great user experience getting 404 when accessing to the build link which it's provided in the Pull Request with the GitHub check `continuous-integration/jenkins/pr-merge`.

In my case, I did use the feature property to use the traditional view but eventually I'd like to move back to the BO view.

Any hints whether this behavior happened previously or is it a regression somehow with the latest release?

Cheers

In my case, I did enable the traditional view by default with