When using homey app on iphone outside Wifi reach, Homey is offline (whatsapp works ok)

When using the Homey app om my IPhone 5S (4g) connecting to Homey fails when I am out of reach of Wifi, Homey reports itself as offline.
On my wifes Iphone 6 (4G) it is working fine, we have the same provider and all settings regarding Wifi, mobile network settings and mobile data for Homey is set are the same.
It must be a setting or problem on my IPhone, but what?
Who can help me with this issue?

Might be an stupid question but does your phone have normal internet when not connected to the home wifi?
Did you try killing the application?
Reboot phone while not connected to the wifi?

Should not be necessary but just to rule things out.

Hi Robin

WhatsApp was working without wifi, but I tested sending a mail and that was not working.

Since all my settings were the same as those of my wife, I followed your advice and rebooted the iPhone Which resolved the issue.

Thanks for helping me out, problem resolved, Chris Werensteijn (The Netherlands)

Closed this topic because u mentioned that rebooting the Iphone solved ur issue. If u want this re-opened plz contact any moderator.