Might they have been showing up as UNAVAILABLE because they were in use?
FWIW, there's an EA station in Providence that's had one stall out of service for a while now. It's pretty obvious which one is bad, particularly at night, because its green lights are out. That signal is likely not present for all out-of-order EA stalls, but it is for some. I haven't encountered many out-of-order Superchargers, so I don't know if there might be other obvious signals of their status.
No, I'm pretty sure that's not the case. At one stop (4 stall) charger #3 was showing as UNAVAILABLE, which at first it was, as there was a car charging at it. We waited for stall #4 to open up, pulled the car into it, and the app properly showed AVAILABLE. We commenced charging, but couldn't pull a consistent charge rate from it. Meanwhile stall #3 opens up. We consider moving to stall #3 to see if we can get a better charge rate, but the app continues to show UNAVAILABLE. Stalls #1 and #2 are in use and #3 sits empty. Finally #2 opens up and we decide to move to it, but just as we unplug, a Bolt pulls up. I try like hell to convince them to use #3 or #4 (the one we are vacating) but they insist that their Bolt pulls the full 350kW (#1 and #2 are 350kW stations). (they even showed me the extra two pins on their connector that they paid extra for that gives them charging to "263" and that they have one of the new Bolts that can do it--yes, I am dead serious here!) They park in stall #3, but grab the connector of #2 as I plant my palm on my forehead--I could not convince them that the two connectors on stall #2 were not independent!
Fortunately #1 opens up so we pull into it--the app correctly shows #1 as AVAILABLE and we are off to the races with a consistent 100kW+ charge rate. Meanwhile a Polestar 2 pulls up and parks in stall #2, not aware of what the Bolt is trying to do by using stall #2's connector. He plugs in and gets a charge going before the Bolt owner is able to activate his connector. Surprise, surprise he couldn't get it to work, so he plugs into #3 after all and gets exactly the 50kW we told him he would get.
At another station (Richmond, VA -- 8 stall) we show up and 3 stations are showing as UNAVAILABLE. We are the only ones at this station for the entire 40 minutes we were there. Now station #6 was actually UNAVAILABLE. The station was at a Windows error screen. But #3 and #4 which also showed UNAVAILABLE looked ready to charge. I can't confirm that they did actually work, of course because we plugged into #7, but in the 5 stations we stopped at, 4 of them had what appeared to be unexplained UNAVAILABLE stations that otherwise looked fine, an in some cases I actually saw other patrons using them both before and after it was empty. So I'm pretty sure it is some glitch with their network communication in their app.