At least since Jenkins version 1.520 (up and including version 1.524) the "Slaves statistics" Dashboard Portlet is broken for me (I've reported it as part of https://issues.jenkins-ci.org/browse/JENKINS-18510 but this seems to be a different issue since its fix doesn't resolve my issue).

I get:

makeStaplerProxy('/$stapler/bound/[snip]','[snip]',['getSlaves','getOnlineSlaves','getOfflineSlaves','getDisconnectedSlaves','getTasksInQueue','getRunningJobs']) function repeat()[snip]

instead of the actual slave statistics, also see attached screenshot.

Inside the HTML source I see:

<script>
var buildStat =
<script src='/adjuncts/e36d976d/org/kohsuke/stapler/json2.js' type='text/javascript'></script>makeStaplerProxy('/$stapler/bound/c6e51a91-6723-4a14-87f6-2c2571322022','19a1540f
-b285-46da-86b7-639d789655ed',['getSlaves','getOnlineSlaves','getOfflineSlaves','getDisconnectedSlaves','getTasksInQueue','getRunningJobs'])
function repeat(){
[...]

Not sure whether that's by intention or not.

FTR: the issue is present in Google Chrome as well as Firefox. The "Build statistics" Dashboard Portlet doesn't report any numbers either, not yet sure whether that's related or not though.