update bluez to >=5.28.2
18.04 ships with a buggy bluez package for now; newer version is available from this PPA: https://launchpad.net/~bluetooth/+archive/ubuntu/bluez:
sudo add-apt-repository ppa:bluetooth/bluez
sudo apt install bluez
workaround for buggy Bluetooth applet (Unity specific?)
This is probably the issue @solstice mentioned - BT menu applet doesn't let me enable Bluetooth after resuming from sleep. No matter if the toggle switch is off or on, the BT icon is disabled, and rfkill output doesn't change:
$ rfkill list
0: phy0: Wireless LAN
Soft blocked: no
Hard blocked: no
12: hci0: Bluetooth
Soft blocked: no
Hard blocked: no
You can toggle BT manually by running (substitute your own ID):
rfkill block 12
rfkill unblock 12
and BT applet should pick it up correctly now. At this point, you should be able to connect to your devices. For now I've hacked it together using a script that does this automatically after resume:
$ cat /lib/systemd/system-sleep/bt
#!/bin/sh
case $1 in
post)
sleep 5
rfkill block `rfkill list | grep hci | cut -d: -f1`
sleep 1
rfkill unblock `rfkill list | grep hci | cut -d: -f1`
;;
esac
The ID number next to hci0 in rfkill list output seems to increment after every suspend/resume. Disabling/enabling BT using the BT menu should change the output ('soft blocked: yes' for BT disabled via menu), but it doesn't. My guess is that the applet remembers the wrong device ID and is thus trying to enable a device that no longer exists.
Best Answer
I had to unpair/pair my device again. Restarting bluetooth service didn't help.