I have been having this problem since the July firmware update that included a Marvell Bluetooth and Network adapter update. Not long after booting, my Bluetooth mouse disconnects but the Bluetooth keyboard remains active for a time. After a while it too disconnects and eventually the adapter itself is no longer recognized (Event viewer says Bluetooth adapter not installed) but WIFI is still active although it apparently uses the same adapter. After many reboots, reinstalls of the OS and trying another Bluetooth mouse and investing in a USB Bluetooth adapter I determined it was the new driver that caused the problem. The newest driver I have is 15.68.17021.121 dated 2021-05-07 and is the one causing the problem. I rolled back to 15.68.17021.116 from 2020-01-21 and it works fine. Note that I needed to roll back the driver for both the Bluetooth adapter and WIFI for this to work. However, being on the Windows Insider program each update rolls these drivers forward even after turning off the update options for them in the driver option and the registry. At one point I thought the adapter itself was failing but obviously not because it works fine with the older driver. I am currently running the latest Dev version of Windows 11 but had previously reinstalled the latest regular version of Windows 10 and it too had the same problem. In all cases of OS reinstall, they were clean with nothing else installed until I tested the Bluetooth functionality. Has anyone else had this same experience with a Surface Pro 2017 or is this just unique to my machine?