Seems to be persistent problem with wireless "magic??" keyboards and mice. Sometimes it "finds"it but other times only a reset return it. The "shift-option" move is not the answer. 2016 IMac
Agreed. Although a wireless Logitech keyboard and mouse are just as good. I've never had any of them get lost from their Unify receiver. Plus unify works immediately on boot like a regular USB keyboard. Unlike Apple's Bluetooth options which sometimes won't connect until the OS starts to load.
With recent macOS versions, if you don''t want your "pets" to get "lost" you need to put them on a leash, as Fishrrman suggests. Bypassing Bluetooth by using a Logitech wireless mouse, and possibly a companion Logitech wireless keyboard, is also a good option. Logitech's wireless tech is much more stable and reliable than the multipurpose Bluetooth.