Making a wild guess that it was a Circle K-station that you went to? They were quite early to the market with fast chargers, and had a lot of reliability issues with some of the chargers. Like you suggested, it's usually software related, and you can often get them to work by just power-cycling them using the emergency stop button. If you hear the loud click from the metal contacts or the charger latches with the port and it doesn't start charging it's almost always a software glitch that a restart will fix.

For regular AC-charging all the logic is in the car, so the only thing you really need is some safety features on the outside, typically some ground fault protection and so on. But when you use a DC fast charger the charger itself and the cars battery management system has to work together, which I imagine can cause all kinds of edge cases where people have interpreted the standards differently. It didn't help that there were multiple different standards early on.

In this case it was indeed Circle-K, but also the Mer stations at the same place. But again, not all of them, just almost all of them.

To be fair though, the Mer stations did say "out of order", was just the Circle-K ones which didn't show correct status.

However, when driving alone you don't have the luxury of checking the app while driving. So in almost all cases you don't find out until you're there.

A 240V AC or whatever EVSE is pretty basic and are generally easy to keep reliable. I doubt your friend is building 1000VDC chargers.

In fact for “L2” charging the charger is part of the car. The thing on the wall/poll is more properly called a “wall box”, and is mostly a contactor that the car can communicate with.

Sure, a supercharger is more complicated than an EVSE. I assume the most complicated part, in terms of hardware, is the AC to DC converter. Though, I have hard time imagining they're still, after years of making these things, having massive reliability issues with the AC-DC converter hardware.

Never had any issues here in Norway, but I only charge on superchargers. Are the others really that bad?

Tesla reliability is much, much, better than any other network. In the nearly seven years that I've been driving my Model S in eight countries the car has never directed me to a charging station that wasn't working. Sometimes it doesn't count out of order stalls correctly but that just means waiting a bit longer for another car to finish charging; even that is exceedingly rare.

Out of interest I occasionally try to charge at a non-Tesla charger and the experience is dismal with a roughly 50% failure rate. Sometimes the charger won't start, sometimes the payment system won't accept my credit card, sometimes the app doesn't work, sometimes the touchscreen is simply not functioning.

But things are definitely improving in the UK at least. But another problem is that the cost of charging at many motorway service station fast chargers makes refuelling about as expensive as driving an ICE car. Tesla is noticeably cheaper than the other networks.

This was all superchargers. Across two different providers no less.

Yet not all of them, so it wasn't a common cause as such.

edit: This was one of the worse cases, but it's not infrequent I experience at least one charger at a station out of service. I would say it's rather seldom I charge on a station where all chargers work.