Lost Slacker after applying latest internet delivered update. Did not come back after multiple resets (both main display and the steering wheel dashboard display). After complaining to the SC they asked if I did the reset with the radio selected on my media. I thought no I did it with Slacker selected (spinning endlessly and never loading a song). I did the reset after selecting the FM radio setting and voila, it worked!
Couldn't find anywhere that specifically required a reboot/reset to be done with certain things selected.
Slacker service as a whole (not just Model S) had some major issues over the weekend. They fixed it all last night. I am thousands of mile from my Model S, but I was having difficult with slacker too. They said their engineers worked all weekend to figure out what was wrong. Basically, on regular slacker service (on my iPad and HTC One), a lot of music/albums were just flat gone out of the inventory.
I think even after that, the apps were messing up a bit, but I think it's gotten better as things naturalize with their service.
Ok, I got Slacker to work. This might work for you if you are on 5.12 (1.64.39).
1. Switch to FM
2. Close the browser.
3. Reboot center screen.
4. Connect to WIFI
5. Open browser and go to a web site (I think this establishes the network connection), wait for page to fully load.
6. Open Slacker
7. Hit Pause, Hit Play, Hit forward.