There is yet another way to make bluetooth devices unusable.

The beluetooth adapter is by default powered off, and has to be manually
powered on to be able to connect devices.

[bluetooth]# scan on
Failed to start discovery: org.bluez.Error.NotReady
[bluetooth]# scan on
Failed to start discovery: org.bluez.Error.NotReady
[bluetooth]# scan on
Failed to start discovery: org.bluez.Error.NotReady
[bluetooth]# power on
[bluetooth]# scan on
Failed to start discovery: org.bluez.Error.NotReady
[bluetooth]# scan on
Failed to start discovery: org.bluez.Error.NotReady
Failed to set power on: org.bluez.Error.Failed
[DEL] Controller 00:E0:3C:87:B8:03 naga [default]
[NEW] Controller 00:E0:3C:87:B8:03 naga [default]
[CHG] Controller 00:E0:3C:87:B8:03 UUIDs: 0000110e-0000-1000-8000-00805f9b34fb
[CHG] Controller 00:E0:3C:87:B8:03 UUIDs: 0000111f-0000-1000-8000-00805f9b34fb
[CHG] Controller 00:E0:3C:87:B8:03 UUIDs: 00001200-0000-1000-8000-00805f9b34fb
[CHG] Controller 00:E0:3C:87:B8:03 UUIDs: 00001112-0000-1000-8000-00805f9b34fb
[CHG] Controller 00:E0:3C:87:B8:03 UUIDs: 00001108-0000-1000-8000-00805f9b34fb
[CHG] Controller 00:E0:3C:87:B8:03 UUIDs: 0000110c-0000-1000-8000-00805f9b34fb
[CHG] Controller 00:E0:3C:87:B8:03 UUIDs: 00001800-0000-1000-8000-00805f9b34fb
[CHG] Controller 00:E0:3C:87:B8:03 UUIDs: 0000110a-0000-1000-8000-00805f9b34fb
[CHG] Controller 00:E0:3C:87:B8:03 UUIDs: 00001801-0000-1000-8000-00805f9b34fb
[CHG] Controller 00:E0:3C:87:B8:03 UUIDs: 0000110b-0000-1000-8000-00805f9b34fb
[CHG] Controller 00:E0:3C:87:B8:03 UUIDs: 0000180a-0000-1000-8000-00805f9b34fb
[bluetooth]# power on
[CHG] Controller 00:E0:3C:87:B8:03 Class: 0x006c010c
Changing power on succeeded
[CHG] Controller 00:E0:3C:87:B8:03 Powered: yes
[bluetooth]# scan on
Discovery started


I think that it's quite clear you wanted your adapter powered on if you tried
to scan for devices.

The Linux kernel got automatic power management ages ago. Can't that apply to
bluetooth as well?