Often with a Linux kernel update, or even after a first install of Linux in place of Windows, Bluetooth stops working and the advice is usually to just power off your computer, wait a bit, and then turn it on again. Bluetooth then miraculously works again.
I mean the issue could also come from other things (not starting the right kernel module etc…), but very often it’s just this simple trick that makes it work again.
So what is changing in the Bluetooth device when you do this power off/wait a bit/power on trick?
Could also be that the Bluetooth kernel module is a loadable one, and if you’ve updated the kernel (which will usually take place pretty soon after a first install) then you won’t have the matching folder of modules to load up until you restart. Arch is a bugger for this - I’ve an external mouse that works fine if you keep it plugged in during a kernel update, but it won’t be recognised after an update until you restart again. Not a big deal - you can choose when to update.
I believe Arch has an optional pacman hook to prevent this.