Bluetooth icon keeps randomly disappearing from menu bar in High Sierra

From some unknown reason, the bluetooth icon keeps disappearing from the menu bar at random. I have to open up settings and activate "Show bluetooth in Menu Bar" regularly. Why does this happen and how can I stop it from disappearing?

Using inductive logic, and under the assumption that you didn't "un-tick" the box, then it must be software. My best guess would be software associated with a device that uses Bluetooth. One way to check that is:

Hold down shiftoption while clicking the BT icon in your menu bar. You should see all the usual options, plus one called Debug. From here, things get version dependent, but you should at least have a Debug option giving you more options to reset the Mac's BT module, or any connected Apple BT devices. Some earlier versions of mac os, prior to 10.13.6, are reported to also have a "BT log" option.

And so this might be the first stop, reset devices one at a time in a process-of-elimination mode.

If you're more conversant with BT, Apple has some tools that might help pinpoint an errant device causing the "un-tick". One of these tools is referenced frequently, and called Bluetooth Explorer.app (download). It's part of Apple's developer's toolkit. Another tool available in the same download is PacketLogger.app. Bluetooth Explorer.app would start on my system (10.13.6), but refused to display the GUI, making it useless. But apparently it does run on some systems, so YMMV. However the PacketLogger.app started without drama. It has features that may help find a particular message or message type - if you know what to look for :)

Yeah, I agree, fairly remote possibility that a BT device is the cause, and that these apps will pinpoint it, but if all else fails...

It sounds like a software issue.

I would reset the NVRAM/PRAM and then see if this prevents the symbol from disappearing.

Shut down your Mac, then turn it on and immediately press and hold these four keys together: Option, Command, P, and R. You can release the keys after about 20 seconds, during which your Mac might appear to restart. You might hear a startup sound.

If your Mac plays a startup sound and you hear it twice, let go. If your Mac doesn't play a sound but you see the Apple logo, then let go.

It should bring your Mac back to the login screen. If so login and then keep your eyes on it to see if it continues.

NVRAM (nonvolatile random-access memory) is a small amount of memory that your Mac uses to store certain settings and access them quickly. PRAM (Parameter RAM) stores similar information, and the steps for resetting NVRAM and PRAM are the same.

Settings that can be stored in NVRAM include sound volume, display resolution, startup-disk selection, time zone, and recent kernel panic information. The settings stored in NVRAM depend on your Mac and the devices that you're using with your Mac.