Viberworking on specific Wi-Fi only

[Windows Central Question]

Greetings. I am having an issue with Viber app where I can use it only on specific Wi-Fi. I was searching for answer and see that router / firewall needs to open specific ports, however my friends using Nokia, iPhone and Android OS are having no issues with this app. Any specific reason why is this happening? Much appreciated for all answers.

 

[Ryujingt3]

Can you tell us more about the wifi network specs that it does work on please? Is this for desktop or mobile? If mobile, does it work using 4G (mobile data), with wifi turned off?

 

[Polaris849]

I have Lumia 640 LTE with Windows 10 Mobile OS upgraded from Windows 8.1 OS.
After I upgraded to latest updates for Win10 I also updated every app to latest versions. Hard Reset done afterwards.
I can select between 2G, 3G, 3G Only and 4G --> I selected 4G
I am not using cellular whatsoever - Wi-Fi only => Wi-Fi turned On
On some Open and Free Wi-Fi I can work with Viber with no issues...on others it's not working. I am not sure however what could be the difference. As I said I have Lumia, so maybe that is an issue on some Wi-Fi router devices? I cannot find out why is this happening and curious that it's working on specific Wi-Fi's.