I suggest you to reinstall the latest Intel® Remote Keyboard Host App version 1.9 into your pc and the latest version in your iphone. I have tested the application with Android and iOS and I see the cursor.
Intel® Remote Keyboard Host App version 1.9
I have a similar problem. I have an iPhone 6 and an Ipad Pro and a BRIX w Intel.....all was working fine for a couple weeks. Now due to an update or something there is no mouse cursor unless I turn on the wireless mouse. If the wireless mouse is off or goes to sleep the cursor disappears.
Uninstalled and reinstalled both client and app. Rebooted several times. I can type and all the windows keys, power etc. work, just no mouse cursor (so pretty much worthless).
In regards to your issue with the cursor, I suggest you verify if your Gigabyte Brix already has the latest BIOS and drivers (Chipset, Graphics, USB and the rest of the drivers.
I suggest you to use Gigabyte support website: