I’ve regularly witnessed strange behaviour on one of our SharePoint environments where the ABOUT screen for an installed SharePoint Add-in shows an error message (like the screen-shot below) of ‘Sorry, apps are turned off’ when you first navigate to it after not doing so for a while (10 mins or more). Doing a web browser refresh on the page normally fixes it, but it was annoying so I invested a bit further.
As I say, doing a web browser refresh normally fixes the issue, but it is a pain to have to do that and so, since it shouldn’t be happening in the first place, I decided to investigate.
After some poking around on the SharePoint servers in our farm, I realised the problem was with one of the web-front-end (WFE) servers. All others seemed to be working fine but most of the app pools were stopped on just one server.
Restarting the app pools fixed the issue, but I have now noticed that the issue seems to return on just that one server each time the machine is patched/rebooted. I’m unsure why only this one server is affected or of the true root cause of the issue, but since the fix is easy enough I abandoned my debugging activities at that point and I just log in and restart the app pools if I ever see the message now!