Using stretch image 2017-07-26 for EV3
(to test Visual Studio Code extension)

After power up, BT is "not available in Brickman". After reboot it is available.

Also happened a few times with a previous version (at least one week ago) when trying to use BT speaker. At that time I didn't pay attention because I was messing with pulseaudio and permissions.

When this happens...
connmanctl technologies doesn't show bluetooth
hciconfig -a shows nothing
dmesg has some "Bluetooth:" messages