Tim Hardwick, MacRumors:

Bluetooth is what your Mac uses to connect to wireless devices like keyboards, mice, trackpads, speakers, and other peripherals. Generally, it’s a reliable technology. At some point however, the chances are you’ll run into difficulty establishing a Bluetooth connection with one or more of your devices.

Most problems can be fixed by unpairing and repairing the Bluetooth device, changing its batteries, rebooting your Mac, or performing an SMC reset. But if none of these methods work, you can always try resetting your Mac’s Bluetooth module. Here’s how to do it in macOS using the hidden Bluetooth Debug menu.

Great tip, well documented.