wi fi – the Wifi stops working after a few minutes and the mobile data stops working until the reset

I just received a new Galaxy J7 Crown, Andriod version 8.0.0, Samsung Experience version 9.0.

Will provide more information about the software versions, as needed.

The phone will continually lose the wifi connection a few minutes after being turned on. The Wi-Fi signal continues to connect to the phone, but the Wi-Fi symbol receives an exclamation point next to it (!) And gives the message "Internet may not be available" when viewing all networks available.

I believe that's the phone itself because all other devices work properly on a modem / router. Did not do much to the modem / router other than changing the password to make sure my device was the only one on the network. I have however tried to change the wireless channels. Originally, it was in auto mode, but I tried using numbers 1, 6 and 11, although we lived in a relatively isolated area without any wireless network near. Therefore, no channel should be congested. There are at most 3 devices that access the Internet from the modem / router at any given time. In addition, I am within 15 m of the modem / router, no walls or windows or other element between it and my phone.

I've tried to forget the network on my device, to change the DNS to 8.8.8.8 and 8.8.4.4, complete factory reset. Keep the Wifi turned on while sleeping IS set to Always. The only thing that makes the wifi work again is to wait more than 10 minutes, or turn it off / on.

As far as mobile data is concerned, I live in an area where signals are weak and I can not get any service before going for a few minutes. On previous devices, the phone would change the signal if necessary, but on this device, no logo (LTE, 3G, 1X, anything like that) will be displayed by the bars and I will not be able to access the network before restart the phone. Airplane mode does NOT work to restore service. Do not disable and reactivate mobile data.

Will provide any necessary information upon request.

Thank you.