They had a badly designed app on which the OP relied. It is more like a BP being printed on paper so cheap that it disintegrates shortly after the scheduled take-off time. (Some outstations are already trialling this. )

I can see what you mean from a pragmatic perspective, but if BA's official view is that "the app is rubbish and you shouldn't rely on it", why bother producing an app at all?

Would it really hurt BA, when abandoning their landside posts, to leave a telephone at the check in desk with an instruction to telephone the gate if assistance is required?