If an end-user has previously opened the glide app, can they re-open it at a different time (without cell service) and fully use the app? For example: Is an instance of the app and data cached on the device? What makes this possible, and how do I enable it?
My app is a list of contacts. It would be nice if my users could access the info when they don’t have cellular data service…
I’d say in general, yes. If they’re only reading data.
Although actual results may vary. The App and data are cached on the device, although I believe that if the App has been force closed or idle in the background for some time, it will try and do a UI refresh when it’s opened. I’m not exactly sure what would happen at that time if there was no network. Easy enough to test though 
Thats the only complaint I get from my users. They are unable to view the data when they don’t have service.