I upgraded from 2.9.3 to 2.9.4 and the plugin was no longer tracking new data.
I have W3 Total Cache installed and I tried clearing the cache after upgrade and it still did not work.
I have JS minify enabled on CloudFlare and I'm not sure if anything in the Slimstat JS code changed. (CloudFlare JS minify worked fine with version 2.9.3)
I went ahead and uninstalled 2.9.4 and I guess this also deleted all stats stored in the database? It's ok because I didn't have many stats tracked. Maybe you can improve the process so uninstalling the plugin keeps the data stored in the database. I just installed this plugin 1 month ago so I am fairly new and I don't really know how the slimstat uninstall process works.
I then installed version 2.9.3 from the WordPress server.
After changing the settings to what I had them on before (JS mode is on), stats were now being tracked like they should be.
There must be something in 2.9.4 that is making it not track stats for me.
I'm not sure what changed in 2.9.4 because 2.9.3 worked perfectly.
Also: I'm not sure if this is a Slimstat bug or an iOS bug, but Slimstat is tracking visits from Safari in iOS 6.1 as "Mac OS X".
Using the Chrome browser app in iOS 6.1 tracks correctly as "iOS".