did another try, this time with all updated plugins, it definitely seems that it is unable to load that endpoint - 404 consistently until restart... I think it is a backend thing. 

cc'ing Vivek Pandey to see if he can make any sense of this. Not a huge thing for right now but would be good to know. 

Vivek Pandey Michael Neale FYI - looks like this is the problem, probably not getting updated when plugins are installed: https://github.com/jenkinsci/blueocean-plugin/blob/master/blueocean-rest/src/main/java/io/jenkins/blueocean/rest/ApiHead.java#L116

Keith Zantow Michael Neale we need to construct api routs lazily, so that it waits till all plugins are loaded.

I think the main problem here is, if a plugin that brings extra routes to /blue/rest/, if its installed, how do we update paths without restarting. At present there doesn't seem to be eventing system in Jenkins plugin manager that sends events such as plugin installed/uninstalled. If we have something like that, we can update api routes dynamically. 

Maybe 

ExtensionListListener.onChange() can be used to update api routes in sync with plugins. 

Old ticket. Not seen this problem in a long time.