Have an Archer A3150 V2, not A10.

Our home wifi network has disappeared on some devices such as e-readers and baby camera, which it was perviously connected to and worked. It is working fine on cellphones and computers. Tried rebooting connection, devices and adding a guest network. The network was never hidden. My modem is about 10 years old, but don't think that's the issue because internet connection is fine. Would this be a hardware issue? Do I need to upgrade?