I've wasted a lot of time dealing with this issue. My finding is that Mediatek RZ series wifi/bt combo adapters (like RZ608) typically supplied with AMD motherboard platforms either have a high defect rate or the driver/firmware is unpolished. The reason why removing power from the system for a few seconds works to make the device function again is because these devices run on standby +5V current over USB, which means under default BIOS settings the device will be on and stuck in its malfunctioning state even if the system is powered off. I have found no permanent fix. The RZ608 on my motherboard continues to crash frequently despite downloading the latest drivers from Mediatek themselves (not motherboard vendor), and it's not an OS issue. BT is just as dead under a Linux distro as in Windows. I'm just going to get an add-in card with an Intel chipset, and avoid buying any products with Mediatek radios in them in the future.