In our company we use the git-flow convention with feature and support branches. For all branches having a "/", e.g. "support/5.6.x" the test result page is not shown.
The link to the test report seems fine and it contains: "https://.../job/support%252F5.6.x/1/testReport"
but when clicking on the link, the following URL is visited: "https://.../job/support%2F5.6.x/1/testReport"
By manually fixing the URL by adding "25", the test report is finally shown. However the detail links on the test page are still broken.
I found a similar issue, but that one seemed to be fixed a long while ago: https://issues.jenkins-ci.org/browse/JENKINS-36154