Well, setting other file permissions can lead to this:
> systemctl status bluetooth.service
...
systemd[1291]: ConfigurationDirectory 'bluetooth' already exists but the mode is different. (File system: 755 ConfigurationDirectoryMode: 555)
...
> sudo journalctl -eu bluetooth
Oct 04 11:35:26 HOST systemd[1]: Bluetooth service was skipped because of a failed condition check (ConditionPathIsDirectory=/sys/class/bluetooth).
Oct 04 11:35:27 HOST systemd[1]: Starting Bluetooth service...
Oct 04 11:35:27 HOST systemd[895]: ConfigurationDirectory 'bluetooth' already exists but the mode is different. (File system: 755 ConfigurationDirectoryMode: 555)
Oct 04 11:35:27 HOST bluetoothd[895]: Bluetooth daemon 5.65
Oct 04 11:35:27 HOST systemd[1]: Started Bluetooth service.
Oct 04 11:35:27 HOST bluetoothd[895]: Starting SDP server
Oct 04 11:35:27 HOST bluetoothd[895]: Bluetooth management interface 1.22 initialized
Modifying systemd’s bluetooth.service unit, i.e. changing the ConfigurationDirectoryMode value from 0555 to 0755, reconciles the /etc/bluetooth directory created by bluez with mode 0755 with the service unit’s key-value setting of 0555. Warnings disappears after the service gets reloaded. However upstream seems to had a reason to have 555 here …
Similar issues:
Most issues with bluetooth are due to the “wrong” set folder permissions!