You should never have this problem and I'll give you the opportunity to tell me whyAndroid 6.0.1. Same here. Means now you have to pay attention to the phone (otherwise you may spend hours thinking you're logged on while in fact you're no longer), which also means you can't focus on something else while waiting for a ping. C r a p.
Edit: I don't receive the notification (or I missed it). I just found I am arbitrarily logged off after 20 or 30 minutes if I don't pay attention.