I was able to fix the Bluetooth/unknown-device mobo issues 🙂 I don't know what happened after installing Windows.... my last option was to unplug the PC from wall, not just turn it off or reboot. This fixed it, using the last 0906 Bios! Bluetooth is back to both Windows and Linux and now also there's no issues listed in the device manager anymore.
About the LGS... this one seems trickier and more of a Logitech/Windows-1703 incompatibility, as other users reported, so I'm not expecting wall unplug to fix it and won't try until Logitech provides an update.
Thanks this worked for me on the Maximus IX Code. Bluetooth would just not pair with anything. After many drivers and a lot of frustration I saw your post and unplugged my PC and now it works fine. So much trouble and such a simple fix. SMH
Same issue in 2023 with Maximus IX Code under Windows 10. Device Manager showing a single error entry. BIOS updates no help, reinstalling drivers no help, rebooting no help. I unplugged the power supply from the wall and waited about 20-30 seconds. Fired the machine back up and the BT device shows up!
Thanks @Dakkor !