Internal API viewer not loading

[shane.do...@gmail.com]

I've recently upgraded a really decrepit Jenkins setup to use new docker images for the controller and nginx. Since doing so, we're not able to view the DSL API viewer, it's stuck as below. 

I found some old references from years ago to this being an issue but that it was fixed in version 1.49 so I'm not sure what's going on (we're using 1.78.1 and Jenkins 2.332.2) . As far as I can tell, nothing is being generated in the Jenkins logs when this is failing, unless I'm looking in the wrong place. I've checked the docker logs for the controller and nginx containers and they are not changing when this is happening.

Has anyone else had this issue? If it's cause by a plugin is there an easy way to find out which one rather than uninstalling hundreds of them one by one?