Haven't noticed any disappearing, we have a 4-socket charger at our local Tesco and it doesn't get used much. For me the problem is that it is untethered, so if you want to use it you have to remember to take your own cable, then faff about plugging it in and getting the app going (which randomly logs you out if it hasn't been used in a while), in the rain, trying to read a stupid name on the charger, then going into Tesco for 20 minutes just to get 2Kwh of juice, or less if the charger decides to stop half way, then having to unlock, unplug and wrap up a now wet and dirty cable (because there's mud on the ground) and put it in your boot all for about 30p worth of free electricity.
It's badly thought out and executed. They should have Type 2 cables attached to them like the Tesla ones, and should just start charging without an app. Until then they are just a novelty.