WhatsApp keep loosing internet connection After I force stop it, and restart whatsapp, every thing works as expected. in five minutes again, it stops working. If I do force stop and restart it, it again starts working. 

I do not change anything or even touch the phone, no other apps are running, even I did factory reset and installed only whats-app, nothing else, but the behaviour is the same, I changed sim card, or wifi network, but nothing seems to change, even as last resort system update to 8.1 didn't change the behaviour, it works and suddenly stops and start working after force stop. 

only that behaviour is consistent.

my question is, how to diagnose this ? or solve this ? all ideas are welcome including changing the damn phone. :)
Troubleshooting

Most connection issues can be resolved by doing the following:


Restart your phone, or turn it off and on.
Update WhatsApp to the latest version available on the Google Play Store
Open your phone's Settings > tap Network &amp; Internet > toggle to turn Airplane mode on and off.
Open your phone's Settings > tap Network &amp; Internet > Data usage > toggle to turn Cellular data on.
Open your phone's Settings > tap Apps &amp; notifications > App info > WhatsApp > Data usage > toggle to turn on Background data.
Open your phone's Settings > Network &amp; Internet > Wi-Fi > toggle to turn Wi-Fi off and on.
Try connecting to different Wi-Fi hotspots.
Make sure Wi-Fi stays on during sleep mode.
Reboot your Wi-Fi router.
Contact your mobile provider and make sure your APN settings are configured correctly.
Upgrade your Android operating system to the latest version available for your phone.
If you're having trouble connecting to WhatsApp while on a Wi-Fi network that you don't normally connect to, contact the network administrator.
If you're on a campus or corporate Wi-Fi that has firewall restrictions in place, contact the network administrator.


  WhatsApp isn't designed to be used with proxy or VPN services, so we can't provide support for those configurations.