I was looking at your motherboard on ASUS's site i see no updated system drivers for Windows 10 and assume the latest Windows 8.1 should be fine, if there were any windows update would check and download them. Thinking this can be a driver issue either with keyboard drivers or conflicting with system drivers, i am not positive.
When you plugged in iphone or USB External device in Device manager it was a yellow triangle next to this device, did you right click and open the properties of that device in question, was it a code 43 ? In device manager when this occurs right click the device and scan for hardware changes. Some is shown here about similar issue if code 43.
https://technet.microsoft.com/en-us/...=ws.10%29.aspx
In some cases i would uninstall the devices from the Device Manager and reboot letting it reinstall those devices again. In Universal Serial Bus Controllers uninstall each USB Hub, USB Mass Storage and USB Root Hub and reboot.
Open the Keyboard in Device Manager and uninstall and reboot and any USB root under Human Interface Device.
Just start off with uninstall of the ones in Universal Serial Bus Controllers and see how this works.
How long has this been going on with this keyboard and other devices, just since you tried an external device thinking that was always the issue ? How long since the upgrade to Windows 10 ? Other member may be right about contacting Logitech if you can about this, this issue might of always been there regardless of operating system for some. I am not sure about using these apple drivers on microsoft windows system just for USB