Why do I lose signal after leaving LTE area?

[AC Question]

Losing signal after leaving LTE area.

Samsung S4 on Bell network in Ontario, Canada. Lately when I leave an LTE coverage area and go into a 3G area I will lose connection. The signal strength indicator will show a ø and I need to restart the phone to get it to work. I have the network mode set to LTE/WCDMA/GSM (auto connect). Is this a device setting error or carrier error?
Thanks