Mobile data not working with unconnected WiFi switched on

[anon(9774204)]

Both me and my wife have Galaxy S6's on the Vodafone network here in the UK. Our phones are on the same software & security versions etc.
She has reported an issue to me on a number of occasions - the issue is that I'm not always with her when she reports it, so I've been unable to replicate it at the same time on my own device.

So, when connected to WiFi everything is fine. She can browse the internet, use social media apps, read email etc.
On a number of occasions however, if she is not connected to a WiFi network, she is unable to use the mobile network data until she switches WiFi off.

Example yesterday, she was on a bus. Her mobile indicated an "H" signal strength and her WiFi icon indicated that it was not connected to a WiFi network. She was unable to browse anything online at all, apps not connecting etc until she switched WiFi off.
At that point everything burst into life using the mobile network.

Has anyone seen anything like this before?
Cheers.

 

[lucianus_luciferus]

her WiFi icon indicated that it was not connected to a WiFi network.

my wif icon only shows up in the status bar when it's connected. when wifi is disconnected there is no icon.
so probably the wifi was connected to a public hotspot that requires authentication via web interface but your wife did not authenticate the result being that the phone was using the wifi connection but the Internet was not working because your wife didn't go through the authentication process.
to try and avoid that you can use smart network switch
switch wifi on then go to settings, wifi, more, smart network switch