Bluetooth suddenly gone on Windows 8.1 - service running, no tray icon, no settings

With no warning, while I was replying to an email in Outlook, bluetooth just went away on my Windows 8.1 tablet (Wacom Cintiq Companion 2). [UPDATE] The problem went away after several hours and various steps the last of which are outlined in my answer below, but comes back quite often, seemingly at random, lasting anything from seconds to minutes to hours.

I've followed the steps on an MS support thread, and the Bluetooth Support service now claims to be running in services.msc (before, it was not running)...

...but the symptoms of my problem are still there, even after restarting the system. These are:

• Bluetooth keyboard lost connection, can't connect


• There used to be a Bluetooth icon in the desktop tray, now it's gone.


• If I open the 'metro-style' Bluetooth Settings page, it shows a blue cog for a few seconds, then either a blank white screen, or the generic 'Personal settings' home page


• If I open the desktop-style 'Change Bluetooth settings', the hardware section is completely empty:

...and if I change anything then click Okay, it says this:

An error occurred while Windows was saving your settings. The Bluetooth device might be unplugged.

This makes no sense because Bluetooth on this device is internal, it can't be unplugged.

The problem is exactly the same if I start up while charging, so it's not an energy saving issue. It stopped working while the device was unplugged, and the device was a normal temperature, so the internal Bluetooth adapter can't have been fried by a power surge or overheating.

Before just now, Bluetooth had worked fine for months - although in the last week or two, there has been a couple of times when the Bluetooth keyboard stopped working for about 10 seconds then started working again.

No updates have been applied recently, and no new software installed.

I can't find anything Bluetooth related in Device Manager to check the drivers (but to be honest I'm not 100% sure where to look). While trying to research this I found a MS answer that prompted me to look at what Bluetooth items I have in Control Panel, I'm not sure if this below is normal or not (I can't see "Bluetooth devices"):

How could Bluetooth just disappear like this? What could have happened, and what can I do?

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Update - this still happens, a lot. Bluetooth comes and goes seemingly randomly. Usually it sorts itself out after a few minutes, but sometimes it doesn't. No apparent pattern regarding when it happens, sometimes it's less than 20 minutes after booting up, sometimes it's after working for an entire day. When Bluetooth goes down like this, the Desktop settings report that it is working, but the COM Ports and Hardware tabs crash out:

Here's what happens if I try to restart the Bluetooth service in services.msc:

Error 1053: The service did not respond to the start or control request in a timely fashion.

Sometimes, after a long time of failing, the Metro-style Bluetooth settings screen appears looking like this, with a never-ending working indicator and no clue what it's trying to do.

Note that the 'metered connection' thing is almost certainly a red herring, it doesn't try to do any setup when I'm not on a metered connection. I'm also almost always on a metered connection and it doesn't usually complain.