Q: Wifi connection problem

After updating to IOS 10.0.1, my iPhone 6 plus could not join the second WiFi network in my home. As I always have phone data on, it joins 4G instead of the network. When I look at Airport, the connections seem fine , but in the menu it says 4G . When I disconnect Phone data, the connection to the Internet goes, as can be see on the fourth image.

Nothing like that happened before the update. I have to add that my MacbookPro and my iPad connect normally to the network.

I have tried everything possible: reset phone, network, several times, to no avail.

As I can join networks, I have been told that my phone is fine, it must be my airport express. But, it works fine as usual with my laptop and my iPad. The only thing the latter don't have is Phone data, on or off.

Could anybody help, I am getting very frustrated....