Using Ubuntu Core devices it is not always possible to access via SSH and bluez usually doesn't start up the bluetooth at boot.
1 - install bluez to allow bluetooth usage: "sudo snap install bluez" 2 - check dongle compatibility "sudo bluez.hciconfig" the log must show up the HCI devices with their state 3 - install bluetooth autosatart "sudo snap install bluetooth-autostart" 4- connect if needed the proper interface: "sudo snap connect bluetooth-autostart:bluetooth-control"
Post any trouble using GitHub: https://github.com/mauringo/autostart-bluetooth-snap
basically this app runs the "hcicconfig hci0 up" command. The command is executed with 5s delay thus, any other process that needs bluetooth must use it after 5s.