But just because I've seen and know about this problem does not mean I know a fix, I only know why. The reason we found out was there was a limit on the number of open connections over cellular connections.
The only reason I and a team of others know this is we developed a GPS tracker back before 2010 and we hit that limit early on.
Your story sounds like that limit.
I recently got a mobile 4G Modem as my main internet connection due to moving to a more rural area. The internet coverage is great, everything works.
BUT. The modem fails to run whatsapp web, when both - PC and phone are connected to it. When refreshing the web page on the PC, it says "Trying to reach phone. Make sure your phone has an active internet connection."
When only PC is connected to the modem, but the phone is using it's own data - everything works flawlessly.
The provider doesn't see any problems on their end.
So, has anyone had the same problem? Are there any suggestions to try?
Of course, I have tried to restart all my devices.