I have no problems on 2.4 band but on 5 gHz band if my phone goes to sleep or if I stop using for a while wifi remains "connected" but signal is lost and phone goes to LTE. If I use continuously the signal is fine. Once phone sleeps wifi says connected but data will return when connection is stable. It is my router and perfectly stable. No other device does this only the Note 9. Is this typical or do I have a defective phone?