Qualcomm Atheros AR3012 Bluetooth not working in Windows 10

If this was caused by a Version Update then for 10 days you can roll it back in Settings>Update & Security>Recovery and then hide it until it matures using the Hide Updates Tool which is explained more here:  

https://www.howtogeek.com/223864/how-to-uninstall-and-block-updates-and-drivers-on-windows-10/.

If that doesn't work you can also Go Back in Repair Mode as shown here:

https://www.tenforums.com/tutorials/2294-advanced-startup-options-boot-windows-10-a.html

 I'll give all possible steps for troubleshooting Bluetooth in order of priority.  Many problems right now are being solved by updating to the latest version so if you want to skip to that step see the Repair Install at bottom:

Try Updating the Bluetooth driver from the PC maker's Support Downloads webpage for your exact model.  Install it even if it's the same or newer than the one in Device Manager reached by right clicking the Start button.

Right click Start button to access Device Manager, locate Bluetooth device (if necessary from View tab Show Hidden Devices), on Driver tab see if Roll Back is available, if not try Update Driver, first automatically, then Browse, then Let Me Pick to try all previously installed Drivers. 

If these fail try to Uninstall the Driver, restart PC to reinstall.

Make sure you're pairing correctly as shown here:  https://support.microsoft.com/en-us/help/15290/windows-connect-bluetooth-device

 See Fixes here which are all working: 

https://support.microsoft.com/en-us/help/14169/windows-10-fix-bluetooth-problems

https://superuser.com/questions/1017867/make-windows-10-recognize-bluetooth-dongle-as-bluetooth

https://answers.microsoft.com/en-us/windows/forum/windows\_10-hardware-winpc/bluetooth-not-working-cant-find-in-device-manager/ccfa2f34-ac5e-4718-b499-e6050e511a41

Try the Bluetooth troubleshooter at Settings > Update & Security > Troubleshoot. 

Try turning off Fast Startup at Settings > System > Power & Sleep > Additional Power Settings > Choose what Power buttons do > Change settings that are unavailable > uncheck Fast Startup. 

If this is a mic or headset right click Volume icon in System Tray to Open Sound Settings,  make sure the correct device is selected for input or output in the dropdown menu. 

Then try pairing again, if necessary run the Bluetooth Troubleshooter again. 

If this was caused by a Version Update then for 10 days you can roll it back in Settings>Update & Security>Recovery and then hide it until it matures using the Hide Updates Tool which is explained more here:  

https://www.howtogeek.com/223864/how-to-uninstall-and-block-updates-and-drivers-on-windows-10/.

If you think the BT adapter has failed, you can replace it easily with a USB nano adapter like this one:   https://www.amazon.com/ZEXMTE-Bluetooth-Receiver-Transfer-Wireless/dp/B0775YF36R/ref=bmx\_1/144-8846981-0178846?\_encoding=UTF8&pd\_rd\_i=B0775YF36R&pd\_rd\_r=fc7fb64f-ee89-4d01-949a-cce053b97603&pd\_rd\_w=re3cN&pd\_rd\_wg=I4GXx&pf\_rd\_p=806524e0-5994-4c0d-9d36-11f6132400bc&pf\_rd\_r=56PQ4YAVKHETB3GJY6BH&psc=1&refRID=56PQ4YAVKHETB3GJY6BH

Go over this checklist to make sure the install is set up correctly, optimized for best performance, and any needed repairs get done:  http://answers.microsoft.com/en-us/windows/wiki/windows\_10-performance/windows-10-performance-and-install-integrity/75529fd4-fac7-4653-893a-dd8cd4b4db00

Start with Step 4 to turn off Startup freeloaders which can conflict and cause issues, then Step 7 to check for infection the most thorough way, then step 10 to check for damaged System Files.  Then continue with the other steps to go over your install most thoroughly. 

If you want to complain to Microsoft use the Feedback Hub app in Start Menu where developers are tasked to process consumer feedback.   But Microsoft will not even see it here because this is a  tech forums where we are mostly volunteers trying to help solve your problems.

Same problem.  Instant failure of the bluetooth as soon as 1909 was forced upon me.  There isn't even a slider anymore to turn it on.  Please stop breaking working computers by forcing people to update bad updates.

You are not talking to Microsoft here but other users like yourself. If you have a problem to report to Microsoft then use the Feedback Hub (winkey+f) and report it directly.

It's always best to get the drivers direct from the manufacturer as windows default drivers may not be up to date or work correctly. I noticed the OP posted on 29 October so that would have been an Insider Preview build as 1909 has only just been released to the general public.

For others with an Intel Bluetooth driver, but the same issue described in OP, install the latest drivers from this location:

https://downloadcenter.intel.com/download/29125/Intel-Wireless-Bluetooth-for-Windows-10

1909 broke Bluetooth for me, but these drivers (21.50.0 version at current) fixed everything for me...

Good luck!

EDIT: also, MS please get your act together with regards to Bluetooth.