This line seems to fail to the ‘else’ clause which doesn’t display the log link:
https://github.com/jenkinsci/pipeline-stage-view-plugin/blob/35de9f668c0aec5bd4560884b61f94f335579987/ui/src/main/js/view/templates/stage-logs.hbs#L4

The odd thing is that if you lookup “this._links.log.href” it does appear as a valid value. You can get these urls from inspecting the html.

 
I suspect it is temporarily null, but i’m not sure why.  The null result gets stored in this plugins caching layer. If I clear the cache and reload the stage view page, the log links get rendered.Manage Jenkins > Script Console

1. print cache
   println(com.cloudbees.workflow.flownode.FlowNodeUtil.CacheExtension.all().get(0).getRunCache().asMap())

1. delete cache
   com.cloudbees.workflow.flownode.FlowNodeUtil.CacheExtension.all().get(0).getRunCache().invalidateAll()