On my grandmas Galaxy J4+, whenever she tries to call someone on Viber or WhatsApp (through WiFi) the calls lasts around 30-60 seconds until WiFi randomly turns off and the call ends. Then I have to turn off the WiFi in the settings of the phone and turn it on again. It’s not a problem with our internet because she can browse the web and watch YT videos without issues. Can someone please help me find the issue, my grandma can’t call any of her relatives and it’s really sad...